Add testing support option to introduce latency

gradle/publish-root-config.gradle

@@ -98,6 +98,7 @@ def publishedProjects = [
         'grails-testing-support-dbcleanup-h2',
         'grails-testing-support-dbcleanup-postgresql',
         'grails-testing-support-http-client',
+        'grails-testing-support-latency',
         'grails-testing-support-mongodb',
         'grails-testing-support-views-gson',
         'grails-testing-support-web',

grails-doc/src/en/guide/introduction/whatsNew.adoc

@@ -105,6 +105,15 @@ Integration tests that implement `HttpClientSupport` can now use `httpPostForm(.
 request bodies. The helper URL-encodes form fields using UTF-8, and repeated values in a `Collection` or array are encoded as
 repeated keys in insertion order.
 
+==== Latency Testing Support
+
+The new `grails-testing-support-latency` module injects artificial latency into the application under test, so that
+requests randomly take longer. Slower responses widen the window in which timing bugs occur, turning intermittently
+flaky functional tests — assertions that race a navigation, missing waits, ordering assumptions — into deterministic
+failures. The module is inert until `grails.testing.latency.enabled` is set to `true`, and the delay range, the
+fraction of requests affected, and the url patterns are all configurable. See the
+xref:testing/functionalTesting[Functional Testing] section for details.
+
 ==== GORM for MongoDB: TTL, Text, and Reconciled Indexes
 
 GORM for MongoDB can now declare a https://www.mongodb.com/docs/manual/core/index-ttl/[TTL index] directly in the mapping DSL.

grails-doc/src/en/guide/testing/functionalTesting.adoc

@@ -88,3 +88,69 @@ class MySpec extends Specification {
 
 }
 ----
+
+
+==== Simulating Latency
+
+Functional tests are prone to timing bugs: an assertion that races a page navigation, a missing
+wait, or an assumption about response ordering may pass reliably on a fast local machine and fail
+intermittently on slower CI infrastructure. The `grails-testing-support-latency` module makes such
+bugs reproducible by injecting artificial latency into the application under test, so that requests
+randomly take longer.
+
+Add the dependency to your integration test configuration:
+
+[source,groovy]
+----
+dependencies {
+    integrationTestRuntimeOnly 'org.apache.grails:grails-testing-support-latency'
+}
+----
+
+The module is inert until enabled. To activate it, set `grails.testing.latency.enabled` to `true`,
+for example in `application.yml` under a test environment, or as a system property on the test JVM:
+
+[source,groovy]
+----
+tasks.named('integrationTest', Test) {
+    systemProperty('grails.testing.latency.enabled', 'true')
+}
+----
+
+When enabled, a servlet filter is registered with the highest precedence that delays each matched
+request by a random amount of time before it is processed, mirroring what a slow network or an
+overloaded server looks like to the browser or HTTP client driving the test.
+
+The following configuration properties are supported under the `grails.testing.latency` prefix:
+
+[format="csv", options="header"]
+|===
+Property,Default Value,Description
+enabled,`false`,Whether to inject artificial latency
+min-delay,`0`,Lower bound (inclusive) of the random delay per request
+max-delay,`2s`,Upper bound (inclusive) of the random delay per request
+probability,`1.0`,Fraction of requests to delay between `0.0` (none) and `1.0` (all)
+url-patterns,`/*`,Servlet url patterns the filter applies to
+seed,none,Optional fixed random seed for reproducible delay sequences
+|===
+
+Durations without a unit suffix are interpreted as milliseconds; suffixes such as `500ms`, `2s` are
+also supported. For example, to delay half of all requests by between a quarter and two seconds:
+
+[source,yaml]
+----
+grails:
+    testing:
+        latency:
+            enabled: true
+            min-delay: 250ms
+            max-delay: 2s
+            probability: 0.5
+----
+
+A useful pattern is a dedicated CI job (or an occasional local run) that executes the functional
+test suite with latency enabled and a generous `max-delay`. Tests that only pass on a fast server —
+for example a Geb assertion that reads the page before a click-triggered navigation completes —
+will fail deterministically under latency instead of flaking rarely in CI.
+
+WARNING: This module is a testing aid. Never enable it in production configuration.

grails-test-examples/latency/build.gradle

@@ -0,0 +1,48 @@
+/*
+ *  Licensed to the Apache Software Foundation (ASF) under one
+ *  or more contributor license agreements.  See the NOTICE file
+ *  distributed with this work for additional information
+ *  regarding copyright ownership.  The ASF licenses this file
+ *  to you under the Apache License, Version 2.0 (the
+ *  "License"); you may not use this file except in compliance
+ *  with the License.  You may obtain a copy of the License at
+ *
+ *    https://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing,
+ *  software distributed under the License is distributed on an
+ *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *  KIND, either express or implied.  See the License for the
+ *  specific language governing permissions and limitations
+ *  under the License.
+ */
+
+plugins {
+    id 'org.apache.grails.buildsrc.properties'
+    id 'org.apache.grails.buildsrc.dependency-validator'
+    id 'org.apache.grails.buildsrc.compile'
+    id 'org.apache.grails.buildsrc.vulnerability-scan'
+}
+
+version = '0.1'
+group = 'latencyapp'
+
+apply plugin: 'org.apache.grails.gradle.grails-web'
+
+dependencies {
+    implementation platform(project(':grails-bom'))
+
+    implementation 'org.apache.grails:grails-dependencies-starter-web'
+    implementation 'com.h2database:h2'
+    implementation 'org.apache.grails:grails-data-hibernate5'
+    runtimeOnly 'com.zaxxer:HikariCP'
+
+    integrationTestImplementation 'org.apache.grails.testing:grails-testing-support-core'
+    integrationTestImplementation project(':grails-testing-support-http-client')
+    integrationTestRuntimeOnly project(':grails-testing-support-latency')
+}
+
+apply {
+    from rootProject.layout.projectDirectory.file('gradle/functional-test-config.gradle')
+    from rootProject.layout.projectDirectory.file('gradle/grails-extension-gradle-config.gradle')
+}

grails-test-examples/latency/grails-app/conf/application.yml

@@ -0,0 +1,47 @@
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+---
+grails:
+    profile: web
+    codegen:
+        defaultPackage: latencyapp
+    mime:
+        types:
+            json:
+              - application/json
+            html:
+              - text/html
+            xml:
+              - text/xml
+              - application/xml
+            all: '*/*'
+
+environments:
+    test:
+        dataSource:
+            dbCreate: create-drop
+            url: jdbc:h2:mem:testDb;DB_CLOSE_DELAY=-1;LOCK_TIMEOUT=10000
+            driverClassName: org.h2.Driver
+            username: sa
+            password: ''
+        grails:
+            testing:
+                latency:
+                    enabled: true
+                    min-delay: 1500ms
+                    max-delay: 3s
+                    url-patterns:
+                      - '/slow/*'

grails-test-examples/latency/grails-app/conf/logback.xml

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+     Licensed to the Apache Software Foundation (ASF) under one
+     or more contributor license agreements.  See the NOTICE file
+     distributed with this work for additional information
+     regarding copyright ownership.  The ASF licenses this file
+     to you under the Apache License, Version 2.0 (the
+     "License"); you may not use this file except in compliance
+     with the License.  You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing,
+     software distributed under the License is distributed on an
+     "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+     KIND, either express or implied.  See the License for the
+     specific language governing permissions and limitations
+     under the License.
+
+-->
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
+        </encoder>
+    </appender>
+    <root level="error">
+        <appender-ref ref="STDOUT"/>
+    </root>
+</configuration>

grails-test-examples/latency/grails-app/controllers/latencyapp/FastController.groovy

@@ -0,0 +1,34 @@
+/*
+ *  Licensed to the Apache Software Foundation (ASF) under one
+ *  or more contributor license agreements.  See the NOTICE file
+ *  distributed with this work for additional information
+ *  regarding copyright ownership.  The ASF licenses this file
+ *  to you under the Apache License, Version 2.0 (the
+ *  "License"); you may not use this file except in compliance
+ *  with the License.  You may obtain a copy of the License at
+ *
+ *    https://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing,
+ *  software distributed under the License is distributed on an
+ *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *  KIND, either express or implied.  See the License for the
+ *  specific language governing permissions and limitations
+ *  under the License.
+ */
+package latencyapp
+
+import grails.compiler.GrailsCompileStatic
+
+/**
+ * Outside the configured {@code grails.testing.latency.url-patterns}, so responses
+ * from this controller are served without artificial delay.
+ */
+@GrailsCompileStatic
+class FastController {
+
+    def ping() {
+        render('pong')
+    }
+
+}

grails-test-examples/latency/grails-app/controllers/latencyapp/SlowController.groovy

@@ -0,0 +1,34 @@
+/*
+ *  Licensed to the Apache Software Foundation (ASF) under one
+ *  or more contributor license agreements.  See the NOTICE file
+ *  distributed with this work for additional information
+ *  regarding copyright ownership.  The ASF licenses this file
+ *  to you under the Apache License, Version 2.0 (the
+ *  "License"); you may not use this file except in compliance
+ *  with the License.  You may obtain a copy of the License at
+ *
+ *    https://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing,
+ *  software distributed under the License is distributed on an
+ *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *  KIND, either express or implied.  See the License for the
+ *  specific language governing permissions and limitations
+ *  under the License.
+ */
+package latencyapp
+
+import grails.compiler.GrailsCompileStatic
+
+/**
+ * Matched by the configured {@code grails.testing.latency.url-patterns}, so responses
+ * from this controller are artificially delayed.
+ */
+@GrailsCompileStatic
+class SlowController {
+
+    def ping() {
+        render('pong')
+    }
+
+}

grails-test-examples/latency/grails-app/controllers/latencyapp/UrlMappings.groovy

@@ -0,0 +1,30 @@
+/*
+ *  Licensed to the Apache Software Foundation (ASF) under one
+ *  or more contributor license agreements.  See the NOTICE file
+ *  distributed with this work for additional information
+ *  regarding copyright ownership.  The ASF licenses this file
+ *  to you under the Apache License, Version 2.0 (the
+ *  "License"); you may not use this file except in compliance
+ *  with the License.  You may obtain a copy of the License at
+ *
+ *    https://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing,
+ *  software distributed under the License is distributed on an
+ *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *  KIND, either express or implied.  See the License for the
+ *  specific language governing permissions and limitations
+ *  under the License.
+ */
+package latencyapp
+
+class UrlMappings {
+
+    static mappings = {
+        "/$controller/$action?/$id?(.$format)?" {
+            constraints {
+            }
+        }
+    }
+
+}

grails-test-examples/latency/grails-app/init/latencyapp/Application.groovy

@@ -0,0 +1,30 @@
+/*
+ *  Licensed to the Apache Software Foundation (ASF) under one
+ *  or more contributor license agreements.  See the NOTICE file
+ *  distributed with this work for additional information
+ *  regarding copyright ownership.  The ASF licenses this file
+ *  to you under the Apache License, Version 2.0 (the
+ *  "License"); you may not use this file except in compliance
+ *  with the License.  You may obtain a copy of the License at
+ *
+ *    https://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing,
+ *  software distributed under the License is distributed on an
+ *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *  KIND, either express or implied.  See the License for the
+ *  specific language governing permissions and limitations
+ *  under the License.
+ */
+package latencyapp
+
+import grails.boot.GrailsApp
+import grails.boot.config.GrailsAutoConfiguration
+
+class Application extends GrailsAutoConfiguration {
+
+    static void main(String[] args) {
+        GrailsApp.run(Application, args)
+    }
+
+}