Forbid empty testing tasks (#36259)

Closes #34820

With this change we allow for no tests being ran in randomized testing
task, and forbid empty testing tasks from the testing conventions task.
We will no longer have to disable the task if all tests are muted.

Author: alpar-t

buildSrc/src/main/groovy/org/elasticsearch/gradle/BuildPlugin.groovy

@@ -864,7 +864,6 @@ class BuildPlugin implements Plugin<Project> {
         project.tasks.withType(RandomizedTestingTask) {task ->
             jvm "${project.runtimeJavaHome}/bin/java"
             parallelism System.getProperty('tests.jvms', project.rootProject.ext.defaultParallel)
-            ifNoTests System.getProperty('tests.ifNoTests', 'fail')
             onNonEmptyWorkDirectory 'wipe'
             leaveTemporary true
 

buildSrc/src/main/java/org/elasticsearch/gradle/precommit/TestingConventionsTasks.java

@@ -25,7 +25,6 @@
 import org.gradle.api.file.FileTree;
 import org.gradle.api.tasks.Input;
 import org.gradle.api.tasks.OutputFile;
-import org.gradle.api.tasks.SkipWhenEmpty;
 import org.gradle.api.tasks.TaskAction;
 import org.gradle.api.tasks.testing.Test;
 import org.gradle.api.tasks.util.PatternFilterable;
@@ -103,6 +102,22 @@ public void doCheck() throws IOException {
             final Map<String, Set<File>> classFilesPerRandomizedTestingTask = classFilesPerRandomizedTestingTask(allTestClassFiles);
             final Map<String, Set<File>> classFilesPerGradleTestTask = classFilesPerGradleTestTask();
 
+            Map<String, Set<Class<?>>> testClassesPerTask =
+                Stream.concat(
+                    classFilesPerGradleTestTask.entrySet().stream(),
+                    classFilesPerRandomizedTestingTask.entrySet().stream()
+                )
+                    .collect(
+                        Collectors.toMap(
+                            Map.Entry::getKey,
+                            entry -> entry.getValue().stream()
+                                .map(classes::get)
+                                .filter(implementsNamingConvention)
+                                .collect(Collectors.toSet())
+                        )
+                    );
+
+
             problems = collectProblems(
                 checkNoneExists(
                     "Test classes implemented by inner classes will not run",
@@ -118,6 +133,16 @@ public void doCheck() throws IOException {
                         .filter(this::seemsLikeATest)
                         .filter(implementsNamingConvention.negate())
                 ),
+                collectProblems(
+                    testClassesPerTask.entrySet().stream()
+                    .map( entry ->
+                        checkAtLeastOneExists(
+                            "test class in " + entry.getKey(),
+                            entry.getValue().stream()
+                        )
+                    )
+                    .collect(Collectors.joining())
+                ),
                 checkNoneExists(
                     "Test classes are not included in any enabled task (" +
                         Stream.concat(
@@ -215,7 +240,6 @@ private Class<? extends Task> getRandomizedTestingTask() {
     }
 
     @Input
-    @SkipWhenEmpty
     public Map<String, File> getTestClassNames() {
         if (testClassNames == null) {
             testClassNames = Boilerplate.getJavaSourceSets(getProject()).getByName("test").getOutput().getClassesDirs()
@@ -243,6 +267,14 @@ private String checkNoneExists(String message, Stream<? extends Class<?>> stream
         }
     }
 
+    private String checkAtLeastOneExists(String message, Stream<? extends Class<?>> stream) {
+        if (stream.findAny().isPresent()) {
+            return "";
+        } else {
+            return "Expected at least one " + message + ", but found none.\n";
+        }
+    }
+
     private boolean seemsLikeATest(Class<?> clazz) {
         try {
             ClassLoader classLoader = clazz.getClassLoader();