diff --git a/.github/PULL_REQUEST_TEMPLATE.md b/.github/PULL_REQUEST_TEMPLATE.md
new file mode 100644
index 0000000..742d2bc
--- /dev/null
+++ b/.github/PULL_REQUEST_TEMPLATE.md
@@ -0,0 +1,16 @@
+<!--
+- Fill in the form below correctly. This will help the Pest team to understand the PR and also work on it.
+-->
+
+### What:
+
+- [ ] Bug Fix
+- [ ] New Feature
+
+### Description:
+
+<!-- describe what your PR is solving -->
+
+### Related:
+
+<!-- link to the issue(s) your PR is solving. If it doesn't exist, remove the "Related" section. -->
diff --git a/.github/workflows/php-cs-fixer.yml b/.github/workflows/php-cs-fixer.yml
deleted file mode 100755
index 0cd6470..0000000
--- a/.github/workflows/php-cs-fixer.yml
+++ /dev/null
@@ -1,31 +0,0 @@
-name:                               Check & fix styling
-
-on:
-    push:
-        branches:
-            - master
-            - dev
-
-jobs:
-    style:
-        runs-on:                    ubuntu-latest
-
-        steps:
-            -   name:               Checkout code
-                uses:               actions/checkout@v2
-
-            -   name:               Fix style
-                uses:               docker://oskarstark/php-cs-fixer-ga
-                with:
-                    args:           --config=.php_cs.dist --allow-risky=yes
-
-            -   name:               Extract branch name
-                shell:              bash
-                run:                echo "##[set-output name=branch;]$(echo ${GITHUB_REF#refs/heads/})"
-                id:                 extract_branch
-
-            -   name:               Commit changes
-                uses:               stefanzweifel/git-auto-commit-action@v2.3.0
-                with:
-                    commit_message: Fix styling
-                    branch:         ${{ steps.extract_branch.outputs.branch }}
diff --git a/.github/workflows/psalm.yml b/.github/workflows/psalm.yml
deleted file mode 100755
index 82b45c6..0000000
--- a/.github/workflows/psalm.yml
+++ /dev/null
@@ -1,33 +0,0 @@
-name:                          Psalm
-
-on:
-    push:
-        paths:
-            - '**.php'
-            - 'psalm.xml'
-
-jobs:
-    psalm:
-        name:                  psalm
-        runs-on:               ubuntu-latest
-        steps:
-            - uses:            actions/checkout@v2
-
-            - name:            Setup PHP
-              uses:            shivammathur/setup-php@v2
-              with:
-                  php-version: '7.4'
-                  extensions:  dom, curl, libxml, mbstring, zip, pcntl, pdo, sqlite, pdo_sqlite, bcmath, soap, intl, gd, exif, iconv, imagick
-                  coverage:    none
-
-            - name:            Cache composer dependencies
-              uses:            actions/cache@v1
-              with:
-                  path:        vendor
-                  key:         composer-${{ hashFiles('composer.lock') }}
-
-            - name:            Run composer require
-              run:             composer require -n --prefer-dist
-
-            - name:            Run psalm
-              run:             ./vendor/bin/psalm -c psalm.xml
diff --git a/.github/workflows/run-tests.yml b/.github/workflows/run-tests.yml
index cb189d2..d87ab00 100755
--- a/.github/workflows/run-tests.yml
+++ b/.github/workflows/run-tests.yml
@@ -1,8 +1,13 @@
 name:                               Run tests
 
 on:
-  push:
   pull_request:
+    paths:
+      - "**.php"
+      - "phpunit.xml"
+      - ".github/workflows/run-tests.yml"
+      - "composer.lock"
+      - "composer.json"
 
 jobs:
     php-tests:
@@ -10,13 +15,13 @@ jobs:
 
         strategy:
             matrix:
-                php:                [7.4, 8.0]
-                laravel:            [8.*]
+                php:                [8.2, 8.3, 8.4]
+                laravel:            [11.*]
                 dependency-version: [prefer-lowest, prefer-stable]
                 os:                 [ubuntu-latest]
                 include:
-                    - laravel:      8.*
-                      testbench:    6.*
+                    - laravel:      11.*
+                      testbench:    9.*
 
         name:                       P${{ matrix.php }} - L${{ matrix.laravel }} - ${{ matrix.dependency-version }} - ${{ matrix.os }}
 
@@ -29,21 +34,12 @@ jobs:
               with:
                   php-version:      ${{ matrix.php }}
                   extensions:       dom, curl, libxml, mbstring, zip, pcntl, pdo, sqlite, pdo_sqlite, bcmath, soap, intl, gd, exif, iconv, imagick
-                  coverage:         none
+                  coverage:         pcov
 
             - name:                 Install dependencies
               run:                  |
                   composer require "laravel/framework:${{ matrix.laravel }}" "orchestra/testbench:${{ matrix.testbench }}" --no-interaction --no-update
                   composer update --${{ matrix.dependency-version }} --prefer-dist --no-interaction --no-suggest
 
-            # - name:               Execute tests
-            #   run:                vendor/bin/phpunit
-
-            - name:                 Send Slack notification
-              uses:                 8398a7/action-slack@v2
-              if:                   failure()
-              with:
-                  status:           ${{ job.status }}
-                  author_name:      ${{ github.actor }}
-              env:
-                SLACK_WEBHOOK_URL:  ${{ secrets.SLACK_WEBHOOK }}
+            - name:               Execute tests
+              run:                composer run-script test
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
deleted file mode 100755
index ba38a6e..0000000
--- a/.pre-commit-config.yaml
+++ /dev/null
@@ -1,14 +0,0 @@
-repos:
--   repo:          https://github.com/digitalpulp/pre-commit-php.git
-    sha:           1.3.0
-    hooks:
-        - id:      php-lint
-        # - id:    php-unit
-        - id:      php-cbf
-          files:   \.(php)$
-          exclude: \.(blade)\.(php)$
-          args:    [--standard=phpcs.xml -p]
-        - id:      php-cs
-          files:   \.(php)$
-          exclude: \.(blade)\.(php)$
-          args:    [--standard=phpcs.xml -p]
diff --git a/.scrutinizer.yml b/.scrutinizer.yml
deleted file mode 100755
index 59dc837..0000000
--- a/.scrutinizer.yml
+++ /dev/null
@@ -1,154 +0,0 @@
-build:
-    environment:
-        php:
-            version: "7.3.7"
-filter:
-    paths:
-        - 'src/*'
-    excluded_paths:
-        - 'config/*'
-tools:
-    php_analyzer: true
-    php_mess_detector: true
-    php_changetracking: true
-    php_loc:
-        excluded_dirs:
-            - vendor
-    php_pdepend:
-        excluded_dirs:
-            - vendor
-            - tests
-checks:
-    php:
-        code_rating: true
-        duplication: true
-        variable_existence: true
-        useless_calls: true
-        use_statement_alias_conflict: true
-        unused_variables: true
-        unused_properties: true
-        unused_parameters: true
-        unused_methods: true
-        unreachable_code: true
-        sql_injection_vulnerabilities: true
-        security_vulnerabilities: true
-        precedence_mistakes: true
-        precedence_in_conditions: true
-        parameter_non_unique: true
-        no_property_on_interface: true
-        no_non_implemented_abstract_methods: true
-        deprecated_code_usage: true
-        closure_use_not_conflicting: true
-        closure_use_modifiable: true
-        avoid_useless_overridden_methods: true
-        avoid_conflicting_incrementers: true
-        assignment_of_null_return: true
-        verify_property_names: true
-        verify_argument_usable_as_reference: true
-        verify_access_scope_valid: true
-        use_self_instead_of_fqcn: true
-        too_many_arguments: true
-        symfony_request_injection: true
-        switch_fallthrough_commented: true
-        spacing_of_function_arguments: true
-        spacing_around_non_conditional_operators: true
-        spacing_around_conditional_operators: true
-        space_after_cast: true
-        single_namespace_per_use: true
-        simplify_boolean_return: true
-        scope_indentation:
-            spaces_per_level: '4'
-        return_doc_comments: true
-        require_scope_for_properties: true
-        require_scope_for_methods: true
-        require_php_tag_first: true
-        require_braces_around_control_structures: true
-        remove_trailing_whitespace: true
-        remove_php_closing_tag: true
-        remove_extra_empty_lines: true
-        psr2_switch_declaration: true
-        psr2_control_structure_declaration: true
-        psr2_class_declaration: true
-        property_assignments: true
-        properties_in_camelcaps: true
-        prefer_while_loop_over_for_loop: true
-        phpunit_assertions: true
-        php5_style_constructor: true
-        parameters_in_camelcaps: true
-        parameter_doc_comments: true
-        return_doc_comment_if_not_inferrable: true
-        param_doc_comment_if_not_inferrable: true
-        overriding_private_members: true
-        optional_parameters_at_the_end: true
-        one_class_per_file: true
-        non_commented_empty_catch_block: true
-        no_unnecessary_if: true
-        no_unnecessary_function_call_in_for_loop: true
-        no_unnecessary_final_modifier: true
-        no_underscore_prefix_in_properties: true
-        no_underscore_prefix_in_methods: true
-        no_trailing_whitespace: true
-        no_space_inside_cast_operator: true
-        no_space_before_semicolon: true
-        no_space_around_object_operator: true
-        no_goto: true
-        no_global_keyword: true
-        no_exit: true
-        no_empty_statements: true
-        no_else_if_statements: true
-        no_duplicate_arguments: true
-        no_debug_code: true
-        no_commented_out_code: true
-        newline_at_end_of_file: true
-        naming_conventions:
-            local_variable: '^[a-z][a-zA-Z0-9]*$'
-            abstract_class_name: ^Abstract|Factory$
-            utility_class_name: 'Utils?$'
-            constant_name: '^[A-Z][A-Z0-9]*(?:_[A-Z0-9]+)*$'
-            property_name: '^[a-z][a-zA-Z0-9]*$'
-            method_name: '^(?:[a-z]|__)[a-zA-Z0-9]*$'
-            parameter_name: '^[a-z][a-zA-Z0-9]*$'
-            interface_name: '^[A-Z][a-zA-Z0-9]*Interface$'
-            type_name: '^[A-Z][a-zA-Z0-9]*$'
-            exception_name: '^[A-Z][a-zA-Z0-9]*Exception$'
-            isser_method_name: '^(?:is|has|should|may|supports|was)'
-        lowercase_php_keywords: true
-        more_specific_types_in_doc_comments: true
-        missing_arguments: true
-        method_calls_on_non_object: true
-        line_length:
-            max_length: '120'
-        lowercase_basic_constants: true
-        instanceof_class_exists: true
-        function_in_camel_caps: true
-        function_body_start_on_new_line: true
-        fix_use_statements:
-            remove_unused: true
-            preserve_multiple: false
-            preserve_blanklines: false
-            order_alphabetically: true
-        foreach_traversable: true
-        foreach_usable_as_reference: true
-        fix_php_opening_tag: true
-        fix_line_ending: true
-        fix_identation_4spaces: true
-        fix_doc_comments: true
-        ensure_lower_case_builtin_functions: true
-        encourage_postdec_operator: true
-        classes_in_camel_caps: true
-        catch_class_exists: true
-        blank_line_after_namespace_declaration: true
-        avoid_usage_of_logical_operators: true
-        avoid_unnecessary_concatenation: true
-        avoid_tab_indentation: true
-        avoid_superglobals: true
-        avoid_perl_style_comments: true
-        avoid_multiple_statements_on_same_line: true
-        avoid_fixme_comments: true
-        avoid_length_functions_in_loops: true
-        avoid_entity_manager_injection: true
-        avoid_duplicate_types: true
-        avoid_corrupting_byteorder_marks: true
-        argument_type_checks: true
-        avoid_aliased_php_functions: true
-        deadlock_detection_in_loops: true
diff --git a/.styleci.yml b/.styleci.yml
deleted file mode 100755
index c3bb259..0000000
--- a/.styleci.yml
+++ /dev/null
@@ -1 +0,0 @@
-preset: laravel
\ No newline at end of file
diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..b7c113f
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,20 @@
+# Release Note for 1.x
+
+## [v1.2.0](https://github.com/pwweb/Copper/compare/v1.1.0...v1.2.0) - 2025-02-12
+
+* 🧑‍🔬 Add support for SI Units and Prefixes by [@rabrowne85](https://github.com/rabrowne85) in [#4](https://github.com/pwweb/Copper/pull/4)
+
+## [v1.1.0](https://github.com/pwweb/Copper/compare/v1.0.1...v1.1.0) - 2023-08-16
+
+* Apply fixes from StyleCI by [@rabrowne85](https://github.com/rabrowne85) in [#2](https://github.com/pwweb/Copper/pull/2)
+* Add types to Copper
+* Drop PHP 7.x support
+
+## [v1.0.1](https://github.com/pwweb/Copper/compare/v1.0.0...v1.0.1) - 2021-01-15
+
+* Correction to Precision for Decimals
+
+## [v1.0.0](https://github.com/pwweb/Copper/compare/v1.0.0...v1.0.1) - 2021-01-15
+
+* First release
+
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..d875abc
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,51 @@
+# CONTRIBUTING
+
+Contributions are welcome, and are accepted via pull requests.
+Please review these guidelines before submitting any pull requests.
+
+## Process
+
+1. Fork the project
+2. Create a new branch
+3. Code, test, commit and push
+4. Open a pull request detailing your changes. Make sure to follow the [template](.github/PULL_REQUEST_TEMPLATE.md)
+
+## Guidelines
+
+* Please ensure the coding style running `composer lint`.
+* Send a coherent commit history, making sure each individual commit in your pull request is meaningful.
+* You may need to [rebase](https://git-scm.com/book/en/v2/Git-Branching-Rebasing) to avoid merge conflicts.
+* Please remember that we follow [SemVer](http://semver.org/).
+
+## Setup
+
+Clone your fork, then install the dev dependencies:
+```bash
+composer install
+```
+## Lint
+
+Lint your code:
+```bash
+composer lint
+```
+## Tests
+Run all tests:
+```bash
+composer test
+```
+
+Check types:
+```bash
+composer test:type:check
+```
+
+Unit tests:
+```bash
+composer test:unit
+```
+
+Integration tests:
+```bash
+composer test:integration
+```
diff --git a/README.md b/README.md
index 059091f..5226729 100755
--- a/README.md
+++ b/README.md
@@ -44,14 +44,15 @@ If you don't provide a `$style` it will default to `NumberFormatter::DECIMAL`. I
 
 Then with this you can format in any of the following ways:
 
-| Format     | Code                        | Output                                                    |
-| ---------- | --------------------------- | --------------------------------------------------------- |
-| Currency   | `$value->currency('GBP')`   | -£1,234.56                                                |
-| Decimal    | `$value->decimal(2)`        | -1,234.56                                                 |
-| Percentage | `$value->percentage()`      | -123,456%                                                 |
-| Scientific | `$value->scientific()`      | -1.23456E3                                                |
+| Format     | Code                       | Output                                                    |
+|------------|----------------------------|-----------------------------------------------------------|
+| Currency   | `$value->currency('GBP')`  | -£1,234.56                                                |
+| Decimal    | `$value->decimal(2)`       | -1,234.56                                                 |
+| Percentage | `$value->percentage()`     | -123,456%                                                 |
+| Scientific | `$value->scientific()`     | -1.23456E3                                                |
 | Accounting | `$value->accounting('GBP')` | (£1,234.56)                                               |
-| SpellOut   | `$value->spellOut()`        | minus one thousand two hundred thirty-four point five six |
+| SpellOut   | `$value->spellOut()`       | minus one thousand two hundred thirty-four point five six |
+| Unit       | `$value->unit(Unit::GRAM)` | 1.234 kg                                                  |
 
 Since the `create()` function returns an instance of `Copper`, you can chain the methods together i.e. `Copper\Copper::create(-1234.56)->currency('EUR')` leads to `-€1,234.56`.
 
@@ -69,7 +70,7 @@ In addition to the base functions there are a few setters and getters:
 
 ## Change log
 
-Please see the [changelog](changelog.md) for more information on what has changed recently.
+Please see the [changelog](CHANGELOG) for more information on what has changed recently.
 
 ## Contributing
 
diff --git a/composer.json b/composer.json
index b39589b..c664639 100755
--- a/composer.json
+++ b/composer.json
@@ -7,7 +7,7 @@
         "format",
         "NumberFormatter"
     ],
-    "homepage": "http://copper.pw-websolutions.com",
+    "homepage": "https://github.com/pwweb/Copper",
     "support": {
         "issues": "https://github.com/pwweb/Copper/issues",
         "source": "https://github.com/pwweb/Copper"
@@ -16,27 +16,29 @@
     "authors": [{
             "name": "Richard Browne",
             "email": "richard.browne@pw-websolutions.com",
-            "homepage": "http://www.pw-websolutions.com"
+            "homepage": "https://www.pw-websolutions.com"
         },
         {
             "name": "Frank Pillukeit",
             "email": "frank.pillukeit@pw-websolutions.com",
-            "homepage": "http://www.pw-websolutions.com"
+            "homepage": "https://www.pw-websolutions.com"
         }
     ],
     "prefer-stable": true,
     "minimum-stability": "dev",
     "require": {
-        "php": "^8.0",
-        "ext-intl": "*"
+        "php": "^8.2",
+        "ext-intl": "*",
+        "laravel/framework": "^11.0"
     },
     "require-dev": {
-        "friendsofphp/php-cs-fixer": "^2.14 || ^3.0",
-        "kylekatarnls/multi-tester": "^1.1",
-        "phpmd/phpmd": "^2.8",
-        "phpunit/phpunit": "^7.5 || ^8.0",
-        "psalm/plugin-laravel": "^1.2",
-        "squizlabs/php_codesniffer": "^3.4"
+        "laravel/pint": "^1.20",
+        "pestphp/pest": "^v3.7.4",
+        "phpstan/phpstan": "^2.1",
+        "phpstan/phpstan-strict-rules": "^2.0",
+        "rector/rector": "^2.0",
+        "squizlabs/php_codesniffer": "^3.4",
+        "thecodingmachine/safe": "3.0.0-alpha1 as 2.5.0"
     },
     "autoload": {
         "psr-4": {
@@ -50,28 +52,31 @@
     },
     "config": {
         "process-timeout": 0,
-        "sort-packages": true
+        "sort-packages": true,
+        "allow-plugins": {
+            "pestphp/pest-plugin": true
+        }
     },
     "scripts": {
+        "refacto": "rector",
+        "lint": "pint",
+        "test:refacto": "rector --dry-run",
+        "test:lint": "pint --test",
+        "test:type:check": "phpstan analyse --ansi --memory-limit=-1 --debug",
+        "test:type:coverage": "php -d memory_limit=-1  ./vendor/bin/pest --coverage --min=100",
+        "test:unit": "php ./vendor/bin/pest --colors=always --exclude-group=integration --compact",
         "test": [
-            "@phpunit",
-            "@style-check"
-        ],
-        "style-check": [
-            "@phpcs",
-            "@phpstan",
-            "@phpmd"
-        ],
-        "phpunit": "phpunit --verbose",
-        "phpcs": "php-cs-fixer fix -v --diff --dry-run",
-        "phpstan": "phpstan analyse --configuration phpstan.neon --level 3 src tests",
-        "phpmd": "phpmd src text /phpmd.xml",
-        "phpdoc": "php phpdoc.php"
+            "@test:refacto",
+            "@test:lint",
+            "@test:type:check",
+            "@test:type:coverage",
+            "@test:unit"
+        ]
     },
     "extra": {
         "laravel": {
             "providers": [
-                "Copper\\Laravel\\ServiceProvider"
+                "Copper\\Laravel\\CopperServiceProvider"
             ]
         }
     }
diff --git a/phpcs.xml b/phpcs.xml
deleted file mode 100755
index d36c903..0000000
--- a/phpcs.xml
+++ /dev/null
@@ -1,63 +0,0 @@
-<?xml version="1.0"?>
-<ruleset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" name="PHP_CodeSniffer" xsi:noNamespaceSchemaLocation="phpcs.xsd">
-    <description>The coding standard for PWWEB/Artomator.</description>
-
-    <file>src</file>
-    <file>config</file>
-
-    <arg name="basepath" value="."/>
-    <arg name="colors"/>
-    <arg name="parallel" value="75"/>
-    <arg value="np"/>
-
-    <!-- Include the PSR standards -->
-    <rule ref="PEAR">
-        <exclude name="PEAR.NamingConventions.ValidFunctionName"/>
-        <exclude name="PEAR.NamingConventions.ValidVariableName"/>
-        <exclude name="PEAR.Commenting.FileComment"/>
-        <exclude name="PEAR.Commenting.ClassComment"/>
-        <exclude name="PEAR.WhiteSpace.ScopeIndent.IncorrectExact"/>
-        <exclude name="Squiz.Commenting.VariableComment.IncorrectVarType"/>
-        <exclude name="Squiz.ControlStructures.ElseIfDeclaration.NotAllowed"/>
-    </rule>
-    <rule ref="PSR1"/>
-    <rule ref="PSR2"/>
-
-    <rule ref="Squiz.Arrays.ArrayBracketSpacing"/>
-    <rule ref="Squiz.ControlStructures.ControlSignature"/>
-    <rule ref="Squiz.ControlStructures.ElseIfDeclaration"/>
-    <rule ref="Squiz.Commenting.EmptyCatchComment"/>
-    <!-- <rule ref="Squiz.Commenting.InlineComment"/> -->
-    <rule ref="Squiz.Commenting.LongConditionClosingComment"/>
-    <rule ref="Squiz.Commenting.PostStatementComment"/>
-    <rule ref="Squiz.Commenting.VariableComment"/>
-    <rule ref="Squiz.Formatting.OperatorBracket"/>
-    <rule ref="Squiz.Functions.FunctionDeclarationArgumentSpacing"/>
-    <rule ref="Squiz.Operators.ComparisonOperatorUsage"/>
-    <rule ref="Squiz.Scope.MethodScope"/>
-    <rule ref="Squiz.WhiteSpace.ControlStructureSpacing"/>
-    <rule ref="Squiz.WhiteSpace.OperatorSpacing"/>
-    <rule ref="Squiz.WhiteSpace.SuperfluousWhitespace"/>
-    <rule ref="Generic.Arrays.DisallowLongArraySyntax"/>
-    <rule ref="Generic.CodeAnalysis.EmptyStatement"/>
-    <rule ref="Generic.Commenting.Todo"/>
-    <rule ref="Generic.Commenting.DocComment"/>
-    <rule ref="Generic.ControlStructures.InlineControlStructure"/>
-    <rule ref="Generic.Formatting.DisallowMultipleStatements"/>
-    <rule ref="Generic.Formatting.SpaceAfterCast"/>
-    <rule ref="Generic.NamingConventions.ConstructorName"/>
-    <rule ref="Generic.PHP.DeprecatedFunctions"/>
-    <rule ref="Generic.PHP.LowerCaseKeyword"/>
-    <rule ref="Generic.Strings.UnnecessaryStringConcat"/>
-    <rule ref="Generic.WhiteSpace.IncrementDecrementSpacing"/>
-
-    <!-- Private methods MUST not be prefixed with an underscore -->
-    <rule ref="PSR2.Methods.MethodDeclaration.Underscore">
-        <type>error</type>
-    </rule>
-
-    <!-- Private properties MUST not be prefixed with an underscore -->
-    <rule ref="PSR2.Classes.PropertyDeclaration.Underscore">
-        <type>error</type>
-    </rule>
-</ruleset>
\ No newline at end of file
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..c061343
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,9 @@
+includes:
+    - vendor/phpstan/phpstan-strict-rules/rules.neon
+
+parameters:
+    level: max
+    paths:
+        - src
+
+    reportUnmatchedIgnoredErrors: true
diff --git a/phpunit.xml b/phpunit.xml
new file mode 100644
index 0000000..fb95829
--- /dev/null
+++ b/phpunit.xml
@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.3/phpunit.xsd"
+         bootstrap="vendor/autoload.php"
+         colors="true"
+>
+    <testsuites>
+        <testsuite name="Test Suite">
+            <directory suffix="Test.php">./tests</directory>
+        </testsuite>
+    </testsuites>
+    <source>
+        <include>
+            <directory suffix=".php">./src</directory>
+        </include>
+        <exclude>
+            <directory suffix=".php">./src/Copper/Laravel</directory>
+        </exclude>
+    </source>
+</phpunit>
diff --git a/pint.json b/pint.json
new file mode 100644
index 0000000..edd174b
--- /dev/null
+++ b/pint.json
@@ -0,0 +1,7 @@
+{
+    "preset": "laravel",
+    "rules": {
+        "yoda_style": true,
+        "declare_strict_types": true
+    }
+}
diff --git a/psalm.xml b/psalm.xml
deleted file mode 100755
index 82f4d49..0000000
--- a/psalm.xml
+++ /dev/null
@@ -1,20 +0,0 @@
-<?xml version="1.0"?>
-<psalm
-    errorLevel="4"
-    findUnusedVariablesAndParams="true"
-    resolveFromConfigFile="true"
-    useDocblockPropertyTypes="true"
-    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xmlns="https://getpsalm.org/schema/config"
-    xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd">
-    <projectFiles>
-        <directory name="src"/>
-        <ignoreFiles>
-            <directory name="vendor"/>
-        </ignoreFiles>
-    </projectFiles>
-
-    <plugins>
-        <pluginClass class="Psalm\LaravelPlugin\Plugin"/>
-    </plugins>
-</psalm>
\ No newline at end of file
diff --git a/rector.php b/rector.php
new file mode 100644
index 0000000..191989d
--- /dev/null
+++ b/rector.php
@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+use Rector\Config\RectorConfig;
+use Rector\TypeDeclaration\Rector\ClassMethod\ReturnNeverTypeRector;
+
+return RectorConfig::configure()
+    ->withPaths([
+        __DIR__.'/src',
+    ])
+    ->withSkip([
+        __DIR__.'/src/Plugins/Parallel/Paratest/WrapperRunner.php',
+        ReturnNeverTypeRector::class,
+    ])
+    ->withPreparedSets(
+        deadCode: true,
+        codeQuality: true,
+        typeDeclarations: true,
+        privatization: true,
+        earlyReturn: true,
+    )
+    ->withPhpSets();
diff --git a/src/Copper/Copper.php b/src/Copper/Copper.php
index 77cb35a..cbc26f8 100755
--- a/src/Copper/Copper.php
+++ b/src/Copper/Copper.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * This file is part of the Copper package.
  *
@@ -11,6 +13,8 @@
 
 namespace Copper;
 
+use Copper\Enums\Prefix;
+use Copper\Enums\Unit;
 use NumberFormatter;
 
 /**
@@ -20,43 +24,31 @@ class Copper
 {
     /**
      * Locale for instance.
-     *
-     * @var string
      */
     public static string $locale = 'en-GB';
 
     /**
      * Formatter instance.
-     *
-     * @var NumberFormatter
      */
     public static NumberFormatter $formatter;
 
     /**
      * Instance of self.
-     *
-     * @var Copper/Copper|null
      */
     public static ?Copper $instance = null;
 
     /**
      * Style of formatter to use.
-     *
-     * @var int
      */
     public static int $style = NumberFormatter::DECIMAL;
 
     /**
      * Value of the number to format.
-     *
-     * @var float
      */
     public static float $value;
 
     /**
      * Default currency value to use.
-     *
-     * @var string
      */
     public static string $defaultCurrency = 'GBP';
 
@@ -70,7 +62,7 @@ class Copper
      */
     public static function create(float|string|null $value = null, ?int $style = null, ?string $locale = null): Copper
     {
-        if (null === self::$instance) {
+        if (! self::$instance instanceof self) {
             self::$instance = new self;
         }
 
@@ -93,9 +85,9 @@ public static function create(float|string|null $value = null, ?int $style = nul
      * Format the number using DECIMAL.
      *
      * @param  int|null  $precision  Precision to use for formatter.
-     * @return string Formatted number.
+     * @return string|bool Formatted number.
      */
-    public static function decimal(?int $precision = null): string
+    public static function decimal(?int $precision = null): string|bool
     {
         if (false === is_null($precision)) {
             self::$formatter->setAttribute(NumberFormatter::FRACTION_DIGITS, $precision);
@@ -111,9 +103,9 @@ public static function decimal(?int $precision = null): string
      * Format the number using CURRENCY.
      *
      * @param  string  $iso  The 3-letter ISO 4217 currency code indicating the currency to use.
-     * @return string Formatted number.
+     * @return string|bool Formatted number.
      */
-    public static function currency(string $iso): string
+    public static function currency(string $iso): string|bool
     {
         if (NumberFormatter::CURRENCY !== self::$style) {
             self::setStyle(NumberFormatter::CURRENCY);
@@ -125,9 +117,9 @@ public static function currency(string $iso): string
     /**
      * Format the number using SPELLOUT.
      *
-     * @return string Formatted number.
+     * @return string|bool Formatted number.
      */
-    public static function spellOut(): string
+    public static function spellOut(): string|bool
     {
         if (NumberFormatter::SPELLOUT !== self::$style) {
             self::setStyle(NumberFormatter::SPELLOUT);
@@ -139,9 +131,9 @@ public static function spellOut(): string
     /**
      * Format the number using PERCENT.
      *
-     * @return string Formatted number.
+     * @return string|bool Formatted number.
      */
-    public static function percentage(): string
+    public static function percentage(): string|bool
     {
         if (NumberFormatter::PERCENT !== self::$style) {
             self::setStyle(NumberFormatter::PERCENT);
@@ -154,9 +146,9 @@ public static function percentage(): string
      * Format the number using CURRENCY_ACCOUNTING.
      *
      * @param  string  $iso  The 3-letter ISO 4217 currency code indicating the currency to use.
-     * @return string Formatted number.
+     * @return string|bool Formatted number.
      */
-    public static function accounting(string $iso): string
+    public static function accounting(string $iso): string|bool
     {
         if (NumberFormatter::CURRENCY_ACCOUNTING !== self::$style) {
             self::setStyle(NumberFormatter::CURRENCY_ACCOUNTING);
@@ -168,9 +160,9 @@ public static function accounting(string $iso): string
     /**
      * Format the number using SCIENTIFIC.
      *
-     * @return string Formatted number.
+     * @return string|bool Formatted number.
      */
-    public static function scientific(): string
+    public static function scientific(): string|bool
     {
         if (NumberFormatter::SCIENTIFIC !== self::$style) {
             self::setStyle(NumberFormatter::SCIENTIFIC);
@@ -179,13 +171,56 @@ public static function scientific(): string
         return self::$formatter->format(self::$value);
     }
 
+    /**
+     * Format the number using SI units and prefixes.
+     *
+     * @param  Unit  $unit  SI Unit to display using.
+     *
+     * @parm bool $usePrefix Set whether to use prefixes.
+     *
+     * @param  bool  $useThrees  Set whether to use only multiples of three in prefixes.
+     * @param  int|null  $precision  Set the precision of the number.
+     * @return string Formatted number.
+     */
+    public static function unit(Unit $unit, bool $usePrefix = true, bool $useThrees = true, ?int $precision = null): string
+    {
+        if (false === is_null($precision)) {
+            self::$formatter->setAttribute(NumberFormatter::FRACTION_DIGITS, $precision);
+        }
+        if (NumberFormatter::DECIMAL !== self::$style) {
+            self::setStyle(NumberFormatter::DECIMAL);
+        }
+
+        $value = self::$value;
+        $exponent = 0;
+
+        if ($usePrefix) {
+            $exponent = (int) (floor(log10(abs($value))));
+
+            if ($useThrees || $exponent >= 3) {
+                $options = [
+                    (int) floor($exponent / 3) * 3,
+                    (int) ceil($exponent / 3) * 3,
+                ];
+                $exponent =
+                    abs($exponent - $options[0]) < abs($options[1] - $exponent)
+                        ? $options[0]
+                        : $options[1];
+            }
+
+            $value /= (10 ** $exponent);
+        }
+
+        return self::$formatter->format($value).' '.Prefix::from($exponent)->symbol().$unit->value;
+    }
+
     /**
      * Set the Locale.
      *
      * @param  string  $locale  Locale in which the number would be formatted.
-     * @return Copper Copper instance.
+     * @return ?Copper Copper instance.
      */
-    public static function setLocale(string $locale): Copper
+    public static function setLocale(string $locale): ?Copper
     {
         self::$locale = $locale;
         self::create();
@@ -207,9 +242,9 @@ public static function getLocale(): string
      * Set the Style.
      *
      * @param  int  $style  Style of the formatting.
-     * @return Copper Copper instance.
+     * @return ?Copper Copper instance.
      */
-    public static function setStyle(int $style): Copper
+    public static function setStyle(int $style): ?Copper
     {
         self::$style = $style;
         self::create();
diff --git a/src/Copper/Enums/Prefix.php b/src/Copper/Enums/Prefix.php
new file mode 100644
index 0000000..865efeb
--- /dev/null
+++ b/src/Copper/Enums/Prefix.php
@@ -0,0 +1,70 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Copper\Enums;
+
+enum Prefix: int
+{
+    case QUETTA = 30;
+    case RONNA = 27;
+    case YOTTA = 24;
+    case ZETTA = 21;
+    case EXA = 18;
+    case PETA = 15;
+    case TERA = 12;
+    case GIGA = 9;
+    case MEGA = 6;
+    case KILO = 3;
+    case HECTO = 2;
+    case DECA = 1;
+    case BASE = 0;
+    case DECI = -1;
+    case CENTI = -2;
+    case MILLI = -3;
+    case MICRO = -6;
+    case NANO = -9;
+    case PICO = -12;
+    case FEMTO = -15;
+    case ATTO = -18;
+    case ZEPTO = -21;
+    case YOCTO = -24;
+    case RONTO = -27;
+    case QUECTO = -30;
+
+    public function symbol(): string
+    {
+        return match ($this) {
+            self::QUETTA => 'Q',
+            self::RONNA => 'R',
+            self::YOTTA => 'Y',
+            self::ZETTA => 'Z',
+            self::EXA => 'E',
+            self::PETA => 'P',
+            self::TERA => 'T',
+            self::GIGA => 'G',
+            self::MEGA => 'M',
+            self::KILO => 'k',
+            self::HECTO => 'h',
+            self::DECA => 'da',
+            self::DECI => 'd',
+            self::CENTI => 'c',
+            self::MILLI => 'm',
+            self::MICRO => '&micro;',
+            self::NANO => 'n',
+            self::PICO => 'p',
+            self::FEMTO => 'f',
+            self::ATTO => 'a',
+            self::ZEPTO => 'z',
+            self::YOCTO => 'y',
+            self::RONTO => 'r',
+            self::QUECTO => 'q',
+            self::BASE => '',
+        };
+    }
+
+    public function multipleOfThree(): bool
+    {
+        return 0 === (abs($this->value) % 3);
+    }
+}
diff --git a/src/Copper/Enums/Unit.php b/src/Copper/Enums/Unit.php
new file mode 100644
index 0000000..d591ee2
--- /dev/null
+++ b/src/Copper/Enums/Unit.php
@@ -0,0 +1,73 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Copper\Enums;
+
+enum Unit: string
+{
+    case SECOND = 's';
+    case METRE = 'm';
+    case GRAM = 'g';
+    case AMPERE = 'A';
+    case KELVIN = 'K';
+    case MOLE = 'mol';
+    case CANDELA = 'cd';
+    case RADIAN = 'rad';
+    case STERADIAN = 'sr';
+    case HERTZ = 'Hz';
+    case NEWTON = 'N';
+    case PASCAL = 'Pa';
+    case JOULE = 'J';
+    case WATT = 'W';
+    case COULOMB = 'C';
+    case VOLT = 'V';
+    case FARAD = 'F';
+    case OHM = '&ohm;';
+    case SIEMENS = 'S';
+    case WEBER = 'Wb';
+    case TESLA = 'T';
+    case HENRY = 'H';
+    case CELSIUS = '&deg;C';
+    case LUMEN = 'lm';
+    case LUX = 'lx';
+    case BECQUEREL = 'Bq';
+    case GRAY = 'Gy';
+    case SIEVERT = 'Sv';
+    case KATAL = 'kat';
+
+    public function name(): string
+    {
+        return match ($this) {
+            self::SECOND => 'Second',
+            self::METRE => 'Metre',
+            self::GRAM => 'Gram',
+            self::AMPERE => 'Ampere',
+            self::KELVIN => 'Kelvin',
+            self::MOLE => 'Mole',
+            self::CANDELA => 'Candela',
+            self::RADIAN => 'Radian',
+            self::STERADIAN => 'Steradian',
+            self::HERTZ => 'Hertz',
+            self::NEWTON => 'Newton',
+            self::PASCAL => 'Pascal',
+            self::JOULE => 'Joule',
+            self::WATT => 'Watt',
+            self::COULOMB => 'Coulomb',
+            self::VOLT => 'Volt',
+            self::FARAD => 'Farad',
+            self::OHM => 'Ohm',
+            self::SIEMENS => 'Siemens',
+            self::WEBER => 'Weber',
+            self::TESLA => 'Tesla',
+            self::HENRY => 'Henry',
+            self::CELSIUS => 'Celsius',
+            self::LUMEN => 'Lumen',
+            self::LUX => 'Lux',
+            self::BECQUEREL => 'Becquerel',
+            self::GRAY => 'Gray',
+            self::SIEVERT => 'Sievert',
+            self::KATAL => 'Katal',
+        };
+    }
+}
diff --git a/src/Copper/Laravel/CopperServiceProvider.php b/src/Copper/Laravel/CopperServiceProvider.php
new file mode 100755
index 0000000..544b19f
--- /dev/null
+++ b/src/Copper/Laravel/CopperServiceProvider.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of the Copper package.
+ *
+ * (c) Richard Browne <richard.browne@pw-websolutions.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Copper\Laravel;
+
+use Copper\Copper;
+use Illuminate\Foundation\Events\LocaleUpdated;
+use Illuminate\Support\Facades\Event;
+use Illuminate\Support\ServiceProvider;
+
+/**
+ * A simple API extension for NumberFormatter.
+ */
+class CopperServiceProvider extends ServiceProvider
+{
+    public function boot(): void
+    {
+        $this->updateLocale();
+
+        Event::listen(LocaleUpdated::class, fn ($event) => $this->updateLocale());
+    }
+
+    public function updateLocale(): void
+    {
+        $app = $this->app;
+        $locale = $app->getLocale();
+        Copper::setLocale($locale);
+    }
+}
diff --git a/src/Copper/Laravel/ServiceProvider.php b/src/Copper/Laravel/ServiceProvider.php
deleted file mode 100755
index ad1fb8a..0000000
--- a/src/Copper/Laravel/ServiceProvider.php
+++ /dev/null
@@ -1,84 +0,0 @@
-<?php
-
-/**
- * This file is part of the Copper package.
- *
- * (c) Richard Browne <richard.browne@pw-websolutions.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Copper\Laravel;
-
-use Copper\Copper;
-use Illuminate\Contracts\Events\Dispatcher as DispatcherContract;
-use Illuminate\Events\Dispatcher;
-use Illuminate\Events\EventDispatcher;
-
-/**
- * A simple API extension for NumberFormatter.
- */
-class ServiceProvider extends \Illuminate\Support\ServiceProvider
-{
-    /**
-     * Service provider boot loader.
-     *
-     * @return void
-     */
-    public function boot()
-    {
-        $this->updateLocale();
-
-        if (false === $this->app->bound('events')) {
-            return;
-        }
-
-        $service = $this;
-        $events = $this->app['events'];
-
-        if (true === $this->isEventDispatcher($events)) {
-            $events->listen(
-                (true === class_exists('Illuminate\Foundation\Events\LocaleUpdated')) ? 'Illuminate\Foundation\Events\LocaleUpdated' : 'locale.changed',
-                function () use ($service) {
-                    $service->updateLocale();
-                }
-            );
-        }
-    }
-
-    /**
-     * Function to update the locale used by Copper.
-     *
-     * @return void
-     */
-    public function updateLocale()
-    {
-        $app = $this->app;
-        $locale = $app->getLocale();
-        Copper::setLocale($locale);
-    }
-
-    /**
-     * Registration function for Laravel <5.3.
-     *
-     * @return void
-     */
-    public function register()
-    {
-        // Needed for Laravel < 5.3 compatibility
-    }
-
-    /**
-     * Check function for Event Dispatcher.
-     *
-     * @param  Illuminate\Contracts\Events\Dispatcher|Illuminate\Events\Dispatcher|Illuminate\Events\EventDispatcher  $instance  Event dispatcher
-     * @return bool
-     */
-    protected function isEventDispatcher($instance)
-    {
-        return $instance instanceof EventDispatcher
-            || $instance instanceof Dispatcher
-            || $instance instanceof DispatcherContract;
-    }
-}
diff --git a/tests/Pest.php b/tests/Pest.php
new file mode 100644
index 0000000..4e6310e
--- /dev/null
+++ b/tests/Pest.php
@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+|--------------------------------------------------------------------------
+| Test Case
+|--------------------------------------------------------------------------
+|
+| The closure you provide to your test functions is always bound to a specific PHPUnit test
+| case class. By default, that class is "PHPUnit\Framework\TestCase". Of course, you may
+| need to change it using the "pest()" function to bind a different classes or traits.
+|
+*/
+
+// pest()->extend(Tests\TestCase::class)->in('Feature');
+
+/*
+|--------------------------------------------------------------------------
+| Expectations
+|--------------------------------------------------------------------------
+|
+| When you're writing tests, you often need to check that values meet certain conditions. The
+| "expect()" function gives you access to a set of "expectations" methods that you can use
+| to assert different things. Of course, you may extend the Expectation API at any time.
+|
+*/
+
+expect()->extend('toBeOne', function () {
+    return $this->toBe(1);
+});
+
+/*
+|--------------------------------------------------------------------------
+| Functions
+|--------------------------------------------------------------------------
+|
+| While Pest is very powerful out-of-the-box, you may have some testing code specific to your
+| project that you don't want to repeat in every file. Here you can also expose helpers as
+| global functions to help you to reduce the number of lines of code in your test files.
+|
+*/
+
+function something()
+{
+    // ..
+}
diff --git a/tests/TestCase.php b/tests/TestCase.php
new file mode 100644
index 0000000..d42f312
--- /dev/null
+++ b/tests/TestCase.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests;
+
+use PHPUnit\Framework\TestCase as BaseTestCase;
+
+abstract class TestCase extends BaseTestCase
+{
+    //
+}
diff --git a/tests/Unit/CopperTest.php b/tests/Unit/CopperTest.php
new file mode 100644
index 0000000..cc3bbc5
--- /dev/null
+++ b/tests/Unit/CopperTest.php
@@ -0,0 +1,102 @@
+<?php
+
+declare(strict_types=1);
+
+use Copper\Copper;
+use Copper\Enums\Unit;
+
+it('creates an instance with default values', function () {
+    $copper = Copper::create();
+    expect($copper)
+        ->toBeInstanceOf(Copper::class)
+        ->and(Copper::getLocale())
+        ->toBe('en-GB')
+        ->and(Copper::getStyle())
+        ->toBe(NumberFormatter::DECIMAL);
+});
+
+it('creates an instance with custom values', function () {
+    $copper = Copper::create(1234.56, NumberFormatter::CURRENCY, 'fr-FR');
+    expect($copper)
+        ->toBeInstanceOf(Copper::class)
+        ->and(Copper::getLocale())
+        ->toBe('fr-FR')
+        ->and(Copper::getStyle())
+        ->toBe(NumberFormatter::CURRENCY);
+});
+
+it('formats a number as decimal', function () {
+    Copper::create(1234.56, locale: 'en-GB');
+    $result = Copper::decimal(2);
+    expect($result)->toBe('1,234.56');
+});
+
+it('formats a number as currency', function () {
+    Copper::create(1234.56);
+    $result = Copper::currency('USD');
+    expect($result)->toBe('US$1,234.56');
+});
+
+it('formats a number as spellout', function () {
+    Copper::create(1234.56);
+    $result = Copper::spellOut();
+    expect($result)->toBe('one thousand two hundred thirty-four point five six');
+});
+
+it('formats a number as percentage', function () {
+    Copper::create(0.56);
+    $result = Copper::percentage();
+    expect($result)->toBe('56%');
+});
+
+it('formats a number as scientific', function () {
+    Copper::create(1234.56);
+    $result = Copper::scientific();
+    expect($result)->toBe('1.23456E3');
+});
+
+it('formats a number as accounting currency', function () {
+    Copper::create(1234.56);
+    $result = Copper::accounting('USD');
+    expect($result)->toBe('US$1,234.56');
+});
+
+it('formats a number with SI units and prefixes', function (float $value, string $output) {
+    Copper::create($value);
+    $result = Copper::unit(Unit::METRE);
+    expect($result)->toBe($output);
+})->with([
+    [123_456.99, '0.123 Mm'],
+    [12_345.67, '12.346 km'],
+    [1_234.56, '1.235 km'],
+    [123.45, '0.123 km'],
+    [12.34, '12.34 m'],
+]);
+
+it('formats a number with SI units and prefixes whilst using the non-multiples of three', function (float $value, string $output) {
+    Copper::create($value);
+    $result = Copper::unit(Unit::METRE, useThrees: false);
+    expect($result)->toBe($output);
+})->with([
+    [123_456.99, '0.123 Mm'],
+    [12_345.67, '12.346 km'],
+    [1_234.56, '1.235 km'],
+    [123.45, '1.234 hm'],
+    [12.34, '1.234 dam'],
+]);
+
+it('formats a number with SI units and prefixes with specific precision', function () {
+    Copper::create(123456);
+    $result = Copper::unit(Unit::METRE, precision: 2);
+    expect($result)->toBe('0.12 Mm');
+});
+
+it('sets and gets the locale', function () {
+    Copper::setLocale('de-DE');
+    expect(Copper::getLocale())->toBe('de-DE');
+});
+
+it('sets and gets the style', function () {
+    Copper::setStyle(NumberFormatter::CURRENCY);
+    expect(Copper::getStyle())->toBe(NumberFormatter::CURRENCY);
+});
diff --git a/tests/Unit/Enums/PrefixTest.php b/tests/Unit/Enums/PrefixTest.php
new file mode 100644
index 0000000..fbd3547
--- /dev/null
+++ b/tests/Unit/Enums/PrefixTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+use Copper\Enums\Prefix;
+
+it('returns correct symbol for each prefix', function (Prefix $prefix, string $expectedSymbol) {
+    expect($prefix->symbol())->toBe($expectedSymbol);
+})->with([
+    [Prefix::QUETTA, 'Q'],
+    [Prefix::RONNA, 'R'],
+    [Prefix::YOTTA, 'Y'],
+    [Prefix::ZETTA, 'Z'],
+    [Prefix::EXA, 'E'],
+    [Prefix::PETA, 'P'],
+    [Prefix::TERA, 'T'],
+    [Prefix::GIGA, 'G'],
+    [Prefix::MEGA, 'M'],
+    [Prefix::KILO, 'k'],
+    [Prefix::HECTO, 'h'],
+    [Prefix::DECA, 'da'],
+    [Prefix::DECI, 'd'],
+    [Prefix::CENTI, 'c'],
+    [Prefix::MILLI, 'm'],
+    [Prefix::MICRO, '&micro;'],
+    [Prefix::NANO, 'n'],
+    [Prefix::PICO, 'p'],
+    [Prefix::FEMTO, 'f'],
+    [Prefix::ATTO, 'a'],
+    [Prefix::ZEPTO, 'z'],
+    [Prefix::YOCTO, 'y'],
+    [Prefix::RONTO, 'r'],
+    [Prefix::QUECTO, 'q'],
+    [Prefix::BASE, ''],
+]);
+
+it('checks if prefix is multiple of three', function (Prefix $prefix, bool $expectedResult) {
+    expect($prefix->multipleOfThree())->toBe($expectedResult);
+})->with([
+    [Prefix::QUETTA, true],
+    [Prefix::RONNA, true],
+    [Prefix::YOTTA, true],
+    [Prefix::ZETTA, true],
+    [Prefix::EXA, true],
+    [Prefix::PETA, true],
+    [Prefix::TERA, true],
+    [Prefix::GIGA, true],
+    [Prefix::MEGA, true],
+    [Prefix::KILO, true],
+    [Prefix::HECTO, false],
+    [Prefix::DECA, false],
+    [Prefix::DECI, false],
+    [Prefix::CENTI, false],
+    [Prefix::MILLI, true],
+    [Prefix::MICRO, true],
+    [Prefix::NANO, true],
+    [Prefix::PICO, true],
+    [Prefix::FEMTO, true],
+    [Prefix::ATTO, true],
+    [Prefix::ZEPTO, true],
+    [Prefix::YOCTO, true],
+    [Prefix::RONTO, true],
+    [Prefix::QUECTO, true],
+    [Prefix::BASE, true],
+]);
diff --git a/tests/Unit/Enums/UnitTest.php b/tests/Unit/Enums/UnitTest.php
new file mode 100644
index 0000000..b69c81d
--- /dev/null
+++ b/tests/Unit/Enums/UnitTest.php
@@ -0,0 +1,60 @@
+<?php
+
+declare(strict_types=1);
+
+use Copper\Copper;
+use Copper\Enums\Unit;
+
+it('returns correct name for each unit', function (Unit $unit, string $expectedName) {
+    expect($unit->name())->toBe($expectedName);
+})->with([
+    [Unit::SECOND, 'Second'],
+    [Unit::METRE, 'Metre'],
+    [Unit::GRAM, 'Gram'],
+    [Unit::AMPERE, 'Ampere'],
+    [Unit::KELVIN, 'Kelvin'],
+    [Unit::MOLE, 'Mole'],
+    [Unit::CANDELA, 'Candela'],
+    [Unit::RADIAN, 'Radian'],
+    [Unit::STERADIAN, 'Steradian'],
+    [Unit::HERTZ, 'Hertz'],
+    [Unit::NEWTON, 'Newton'],
+    [Unit::PASCAL, 'Pascal'],
+    [Unit::JOULE, 'Joule'],
+    [Unit::WATT, 'Watt'],
+    [Unit::COULOMB, 'Coulomb'],
+    [Unit::VOLT, 'Volt'],
+    [Unit::FARAD, 'Farad'],
+    [Unit::OHM, 'Ohm'],
+    [Unit::SIEMENS, 'Siemens'],
+    [Unit::WEBER, 'Weber'],
+    [Unit::TESLA, 'Tesla'],
+    [Unit::HENRY, 'Henry'],
+    [Unit::CELSIUS, 'Celsius'],
+    [Unit::LUMEN, 'Lumen'],
+    [Unit::LUX, 'Lux'],
+    [Unit::BECQUEREL, 'Becquerel'],
+    [Unit::GRAY, 'Gray'],
+    [Unit::SIEVERT, 'Sievert'],
+    [Unit::KATAL, 'Katal'],
+]);
+
+it('throws exception for invalid unit conversion', function () {
+    expect(fn () => Copper::create(1234.56)->unit('invalid_unit'))
+        ->toThrow(TypeError::class);
+});
+
+it('formats a number with SI units and prefixes for edge cases', function (float $value, string $output) {
+    Copper::create($value);
+    $result = Copper::unit(Unit::METRE);
+    expect($result)->toBe($output);
+})->with([
+    [0.001, '1 mm'],
+    [0.000001, '1 &micro;m'],
+    [0.000000001, '1 nm'],
+    [0.000000000001, '1 pm'],
+    [0.000000000000001, '1 fm'],
+    [0.000000000000000001, '1 am'],
+    [0.000000000000000000001, '1 zm'],
+    [0.000000000000000000000001, '1 ym'],
+]);