Fix JGiven Plugin to be a cacheable task

jgiven-gradle-plugin/build.gradle

@@ -1,6 +1,7 @@
 plugins {
     id "java-gradle-plugin"
     id "com.gradle.plugin-publish" version "0.10.1"
+    id "groovy"
 }
 
 dependencies {
@@ -9,8 +10,9 @@ dependencies {
     implementation "com.google.guava:guava:$guavaVersion"
     implementation "com.google.code.gson:gson:$gsonVersion"
 
-    testImplementation gradleTestKit()
     testImplementation project(':jgiven-junit')
+    testImplementation 'org.spockframework:spock-core:1.3-groovy-2.5'
+
 }
 
 gradlePlugin {

jgiven-gradle-plugin/src/main/java/com/tngtech/jgiven/gradle/JGivenPlugin.java

@@ -6,6 +6,7 @@
 import org.gradle.api.Action;
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
+import org.gradle.api.Task;
 import org.gradle.api.internal.ConventionMapping;
 import org.gradle.api.internal.IConventionAware;
 import org.gradle.api.plugins.ReportingBasePlugin;
@@ -18,19 +19,19 @@
 
 public class JGivenPlugin implements Plugin<Project> {
     @Override
-    public void apply( final Project project ) {
+    public void apply( final Project project ){
         project.getPluginManager().apply( ReportingBasePlugin.class );
 
         addTaskExtension( project );
         addDefaultReports( project );
         configureJGivenReportDefaults( project );
     }
 
-    private void addTaskExtension( Project project ) {
+    private void addTaskExtension( Project project ){
         project.getTasks().withType( Test.class, this::applyTo );
     }
 
-    private void applyTo( Test test ) {
+    private void applyTo( Test test ){
         final String testName = test.getName();
         final JGivenTaskExtension extension = test.getExtensions().create( "jgiven", JGivenTaskExtension.class );
         final Project project = test.getProject();
@@ -42,45 +43,42 @@ private void applyTo( Test test ) {
             test.getOutputs().dir( resultsDir ).withPropertyName( "jgiven.resultsDir" );
         }
 
-        test.prependParallelSafeAction( task ->
-                ( (Test) task ).systemProperty( Config.JGIVEN_REPORT_DIR, extension.getResultsDir().getAbsolutePath() ) );
+        // Java lambda classes are created at runtime with a non-deterministic classname.
+        // Therefore, the class name does not identify the implementation of the lambda and changes between different Gradle runs.
+        // https://docs.gradle.org/current/userguide/more_about_tasks.html#sec:how_does_it_work
+        test.prependParallelSafeAction( new Action<Task>() {
+            @Override
+            public void execute( Task task ){
+                ((Test) task).systemProperty( Config.JGIVEN_REPORT_DIR, extension.getResultsDir().getAbsolutePath() );
+            }
+        } );
     }
 
-    private void configureJGivenReportDefaults( Project project ) {
-        project.getTasks().withType( JGivenReportTask.class,
-                reportTask -> reportTask.getReports().all( (Action<Report>) report -> {
-                    ConventionMapping mapping = ( (IConventionAware) report ).getConventionMapping();
-                    mapping.map( "enabled", new Callable<Boolean>() {
-                        @Override
-                        public Boolean call() {
-                            return report.getName().equals( JGivenHtmlReportImpl.NAME );
-                        }
-                    } );
-                } ) );
+    private void configureJGivenReportDefaults( Project project ){
+        project.getTasks().withType( JGivenReportTask.class, reportTask -> reportTask.getReports().all( (Action<Report>) report -> {
+            ConventionMapping mapping = ( (IConventionAware) report ).getConventionMapping();
+            mapping.map( "enabled", (Callable<Boolean>) () -> report.getName().equals( JGivenHtmlReportImpl.NAME ) );
+        } ) );
     }
 
-    private void addDefaultReports( final Project project ) {
+    private void addDefaultReports( final Project project ){
         final ReportingExtension reportingExtension = project.getExtensions().findByType( ReportingExtension.class );
-        project.getTasks().withType( Test.class,
-                test -> {
-                    JGivenReportTask reportTask = project.getTasks()
-                            .create( "jgiven" + WordUtil.capitalize( test.getName() ) + "Report", JGivenReportTask.class );
-                    configureDefaultReportTask( test, reportTask, reportingExtension );
-                } );
+        project.getTasks().withType( Test.class, test -> {
+            final JGivenReportTask reportTask = project.getTasks()
+                    .create( "jgiven" + WordUtil.capitalize( test.getName() ) + "Report", JGivenReportTask.class );
+            configureDefaultReportTask( test, reportTask, reportingExtension );
+        } );
     }
 
     private void configureDefaultReportTask( final Test test, JGivenReportTask reportTask,
-            final ReportingExtension reportingExtension ) {
+            final ReportingExtension reportingExtension ){
         ConventionMapping mapping = ( (IConventionAware) reportTask ).getConventionMapping();
-        mapping.map( "results",
-                (Callable<File>) () -> test.getExtensions().getByType( JGivenTaskExtension.class ).getResultsDir() );
-        mapping.getConventionValue( reportTask.getReports(), "reports", false ).all( new Action<Report>() {
-            @Override
-            public void execute( final Report report ) {
-                ConventionMapping reportMapping = ( (IConventionAware) report ).getConventionMapping();
-                reportMapping.map( "destination",
-                        (Callable<File>) () -> reportingExtension.file( "jgiven" + "/" + test.getName() + "/" + report.getName() ) );
-            }
-        } );
+        mapping.map( "results", (Callable<File>) () -> test.getExtensions().getByType( JGivenTaskExtension.class ).getResultsDir() );
+        mapping.getConventionValue( reportTask.getReports(), "reports", false )
+                .all( (Action<Report>) report -> {
+                    ConventionMapping reportMapping = ( (IConventionAware) report ).getConventionMapping();
+                    reportMapping.map( "destination",
+                            (Callable<File>) () -> reportingExtension.file( "jgiven" + "/" + test.getName() + "/" + report.getName() ) );
+                } );
     }
 }

jgiven-gradle-plugin/src/test/groovy/com/tngtech.jgiven.gradle/JGivenPluginShould.groovy

@@ -0,0 +1,67 @@
+package com.tngtech.jgiven.gradle
+
+
+import com.google.common.io.Resources
+import org.gradle.testkit.runner.GradleRunner
+import org.junit.Rule
+import org.junit.rules.TemporaryFolder
+import spock.lang.Specification
+
+import static org.gradle.testkit.runner.TaskOutcome.FROM_CACHE
+import static org.gradle.testkit.runner.TaskOutcome.SUCCESS
+
+class JGivenPluginShould extends Specification {
+
+    @Rule
+    TemporaryFolder testProjectDir = new TemporaryFolder()
+    File buildFile
+
+    def setup() {
+        buildFile = testProjectDir.newFile('build.gradle')
+    }
+
+    def "test is cacheable"() {
+        given:
+        buildFile << """
+        plugins {
+            id 'java'
+            id 'com.tngtech.jgiven.gradle-plugin'
+        }
+
+       repositories { jcenter() }
+       dependencies {
+         testImplementation 'com.tngtech.jgiven:jgiven-junit:1.0.0-RC4' 
+         testImplementation 'junit:junit:4.12'
+        }
+    """
+
+        testProjectDir.newFolder("src", "test", "java")
+        File scenario = testProjectDir.newFile("src/test/java/SimpleScenario.java")
+        scenario << Resources.toByteArray(Resources.getResource("SimpleScenario.java"))
+
+        when:
+        def result = GradleRunner.create()
+                .withProjectDir(testProjectDir.getRoot())
+                .withArguments("--build-cache", "test", "jgivenTestReport")
+                .withPluginClasspath()
+                .build()
+
+        then:
+        result.task(":test").outcome == SUCCESS
+        result.task(":jgivenTestReport").outcome == SUCCESS
+
+        when:
+        new File(testProjectDir.root, 'build').deleteDir()
+        result = GradleRunner.create()
+                .withProjectDir(testProjectDir.getRoot())
+                .withArguments("--build-cache", "test", "jgivenTestReport")
+                .withPluginClasspath()
+                .build()
+
+
+        then:
+        result.task(":test").outcome == FROM_CACHE
+        result.task(":jgivenTestReport").outcome == FROM_CACHE
+
+    }
+}