ci: add run conformance command (GoogleCloudPlatform#124)

Adds command to run conformance tests.

- Adds `run_conformance_tests.sh`
- Adds detailed docs about setting up Java and contributing to this repo

Very similar to the Go setup, with a few minor modifications.

<details><summary>FULL LOGS</summary>
<p>

```
./run_conformance_tests.sh
Defaulting to v1.2.0 client.
Use './run_conformance_tests vX.X.X' to specify a specific release version.

========== INSTALLING CLIENT@v1.2.0 ==========
Note: only works with Go 1.16+ by default, see run_conformance_tests.sh for more information.
Done installing client@v1.2.0

========== HTTP CONFORMANCE TESTS ==========
2021/10/26 17:29:46 Validating for http...
2021/10/26 17:29:46 Framework server started.
2021/10/26 17:29:51 HTTP validation started...
2021/10/26 17:29:51 HTTP validation passed!
2021/10/26 17:29:51 Framework server shut down. Wrote logs to /var/folders/27/9q8h1w651z91hycvdf4qf0h0009rgz/T/serverlog_stdout.txt and /var/folders/27/9q8h1w651z91hycvdf4qf0h0009rgz/T/serverlog_stderr.txt.
2021/10/26 17:29:51 All validation passed!

========== BACKGROUND EVENT CONFORMANCE TESTS ==========
2021/10/26 17:29:51 Validating for legacyevent...
2021/10/26 17:29:51 Framework server started.
2021/10/26 17:29:56 Legacy event validation with legacy event requests...
2021/10/26 17:29:56 Events tried:
        - firebase-auth (PASSED)
        - firebase-db1 (PASSED)
        - firebase-db2 (PASSED)
        - firebase-db3 (PASSED)
        - firebase-db4 (PASSED)
        - firebase-db5 (PASSED)
        - firebase-db6 (PASSED)
        - firebase-db7 (PASSED)
        - firebase-db8 (PASSED)
        - firebase-dbdelete1 (PASSED)
        - firebase-dbdelete2 (PASSED)
        - firestore_complex (PASSED)
        - firestore_simple (PASSED)
        - legacy_pubsub (PASSED)
        - pubsub_binary (PASSED)
        - pubsub_text (PASSED)
        - storage (PASSED)
2021/10/26 17:29:56 Legacy event validation passed!
2021/10/26 17:29:56 Framework server shut down. Wrote logs to /var/folders/27/9q8h1w651z91hycvdf4qf0h0009rgz/T/serverlog_stdout.txt and /var/folders/27/9q8h1w651z91hycvdf4qf0h0009rgz/T/serverlog_stderr.txt.
2021/10/26 17:29:56 All validation passed!

========== CLOUDEVENT CONFORMANCE TESTS ==========
2021/10/26 17:29:56 Validating for cloudevent...
2021/10/26 17:29:56 Framework server started.
2021/10/26 17:30:01 CloudEvent validation with CloudEvent requests...
2021/10/26 17:30:01 Events tried:
        - firebase-auth (PASSED)
        - firebase-db1 (PASSED)
        - firebase-db2 (PASSED)
        - firebase-db3 (PASSED)
        - firebase-db4 (PASSED)
        - firebase-db5 (PASSED)
        - firebase-db6 (PASSED)
        - firebase-db7 (PASSED)
        - firebase-db8 (PASSED)
        - firebase-dbdelete1 (PASSED)
        - firebase-dbdelete2 (PASSED)
        - firestore_complex (PASSED)
        - firestore_simple (PASSED)
        - legacy_pubsub (PASSED)
        - pubsub_binary (PASSED)
        - pubsub_text (PASSED)
        - storage (PASSED)
2021/10/26 17:30:01 CloudEvent validation passed!
2021/10/26 17:30:01 Framework server shut down. Wrote logs to /var/folders/27/9q8h1w651z91hycvdf4qf0h0009rgz/T/serverlog_stdout.txt and /var/folders/27/9q8h1w651z91hycvdf4qf0h0009rgz/T/serverlog_stderr.txt.
2021/10/26 17:30:01 All validation passed!
```

</p>
</details>

Author: grant

CONTRIBUTING.md

@@ -31,21 +31,21 @@ Guidelines](https://opensource.google.com/conduct/).
 
 This project is divided into multiple packages, primarily:
 
-- [`functions-framework-api`](./functions-framework-api)
-  - `core`
-  - `testfunction`
-  - `function-maven-plugin`
-  - `conformance`
+- [`functions-framework-api`](./functions-framework-api) – The interfaces for functions.
 - [`java-function-invoker`](./invoker)
+  - `core` - The function invoker
+  - `testfunction` - A set of test functions
+  - `function-maven-plugin` - The Maven plugin for building functions
+  - `conformance` - A set of functions used for conformance testing
 
 ### Setup JDK 11 / 17
 
 Install JDK 11 and 17. One way to install these is through [SDK man](https://sdkman.io/).
 
 ```sh
 sdk install java 11.0.2-open
-sdk install java 17
-sdk use java 17
+sdk install java 17-open
+sdk use java 17-open
 sdk use java 11.0.2-open
 ```
 
@@ -72,3 +72,11 @@ formatting tool locally using one of the options provided at
 cd invoker;
 mvn test;
 ```
+
+### Running Conformance Tests Locally
+
+First, install Go 1.16+, then run the conformance tests with this script:
+
+```
+./run_conformance_tests.sh
+```

run_conformance_tests.sh

@@ -0,0 +1,48 @@
+#!/bin/bash
+# Runs the conformance tests locally from https://github.com/GoogleCloudPlatform/functions-framework-conformance
+#
+# Servers may fail to shutdown between tests on error, leaving port 8080 bound.
+# You can see what's running on port 8080 by running `lsof -i :8080`. You can
+# run `kill -9 <PID>` to terminate a process.
+#
+# USAGE:
+# ./run_conformance_tests.sh [client_version]
+#
+# client_version (optional):
+# The version of the conformance tests client to use, formatted as "vX.X.X".
+# Defaults to the latest version of the repo, which may be ahead of the
+# latest release.
+
+CLIENT_VERSION=$1
+if [ $CLIENT_VERSION ]; then
+    CLIENT_VERSION="@$CLIENT_VERSION"
+else
+    echo "Defaulting to v1.2.0 client."
+    echo "Use './run_conformance_tests vX.X.X' to specify a specific release version."
+    CLIENT_VERSION="@v1.2.0"
+fi
+
+function print_header() {
+    echo
+    echo "========== $1 =========="
+}
+
+# Fail if any command fails
+set -e
+
+print_header "INSTALLING CLIENT$CLIENT_VERSION"
+echo "Note: only works with Go 1.16+ by default, see run_conformance_tests.sh for more information."
+# Go install @version only works on go 1.16+, if using a lower Go version
+# replace command with:
+# go get github.com/GoogleCloudPlatform/functions-framework-conformance/client$CLIENT_VERSION && go install github.com/GoogleCloudPlatform/functions-framework-conformance/client
+go install github.com/GoogleCloudPlatform/functions-framework-conformance/client$CLIENT_VERSION
+echo "Done installing client$CLIENT_VERSION"
+
+print_header "HTTP CONFORMANCE TESTS"
+client -buildpacks=false -type=http -cmd='mvn -f invoker/conformance/pom.xml function:run -Drun.functionTarget=com.google.cloud.functions.conformance.HttpConformanceFunction' -start-delay 5
+
+print_header "BACKGROUND EVENT CONFORMANCE TESTS"
+client -buildpacks=false -type=legacyevent -cmd='mvn -f invoker/conformance/pom.xml function:run -Drun.functionTarget=com.google.cloud.functions.conformance.BackgroundEventConformanceFunction' -start-delay 5 -validate-mapping=false
+
+print_header "CLOUDEVENT CONFORMANCE TESTS"
+client -buildpacks=false -type=cloudevent -cmd='mvn -f invoker/conformance/pom.xml function:run -Drun.functionTarget=com.google.cloud.functions.conformance.CloudEventsConformanceFunction' -start-delay 5 -validate-mapping=false