Add 'TaskLockService'

Resolves #39

Author: jjohannes

src/main/java/org/gradlex/javamodule/testing/TaskLockService.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright the GradleX team.
+ *
+ * Licensed 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.
+ */
+
+package org.gradlex.javamodule.testing;
+
+import org.gradle.api.services.BuildService;
+import org.gradle.api.services.BuildServiceParameters;
+
+/**
+ * No-op service that can serve as 'lock' to prevent multiple test tasks from running in parallel:
+ * usesService(gradle.sharedServices.registerIfAbsent(TaskLockService.NAME, TaskLockService::class) { maxParallelUsages = 1 })
+ */
+public abstract class TaskLockService implements BuildService<BuildServiceParameters.None> {
+    public static String NAME = "taskLock";
+}

src/test/groovy/org/gradlex/javamodule/testing/test/CustomizationTest.groovy

@@ -75,4 +75,30 @@ class CustomizationTest extends Specification {
         then:
         result.task(":app:test").outcome == TaskOutcome.SUCCESS
     }
+
+    def "can use task lock service"() {
+        given:
+        appBuildFile.text = 'import org.gradlex.javamodule.testing.TaskLockService\n\n' + appBuildFile.text
+        appBuildFile << '''
+            javaModuleTesting.whitebox(testing.suites.getByName<JvmTestSuite>("test") {
+                targets.all {
+                    testTask {
+                        usesService(gradle.sharedServices.registerIfAbsent(TaskLockService.NAME, TaskLockService::class) { maxParallelUsages = 1 })
+                    }
+                }
+            }) {
+                requires.add("org.junit.jupiter.api")
+            }
+        '''
+        appModuleInfoFile << '''
+            module org.example.app {
+            }
+        '''
+
+        when:
+        def result = runTests()
+
+        then:
+        result.task(":app:test").outcome == TaskOutcome.SUCCESS
+    }
 }