[Build] Update InternalTestArtifact plugin to reference unique artifacts (elastic#138970) (elastic#139037)

* [Build] Update InternalTestArtifact plugin to reference unique artifacts

This ensures that we can reference multiple test artfiacts of the same type (e.g. javaRestTest) by taking the group name into account for the
referenced capability

* Fix testFixture shortcut

* Fix test fixture capability references

Author: breskeby

BUILDING.md

@@ -239,7 +239,7 @@ similar to how the Gradle build-in `java-test-fixtures` plugin works.
 ```
 dependencies {
   testImplementation(project(":fixture-providing-project')) {
-    requireCapabilities("org.elasticsearch.gradle:fixture-providing-project-test-artifacts")
+    requireCapabilities(${project(":fixture-providing-project').group}:fixture-providing-project-test-artifacts")
   }
 }
 ```

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/InternalTestArtifactExtension.java

@@ -34,7 +34,7 @@ public void registerTestArtifactFromSourceSet(SourceSet sourceSet) {
         JavaPluginExtension javaPluginExtension = project.getExtensions().getByType(JavaPluginExtension.class);
         javaPluginExtension.registerFeature(name + "Artifacts", featureSpec -> {
             featureSpec.usingSourceSet(sourceSet);
-            featureSpec.capability("org.elasticsearch.gradle", project.getName() + "-" + sourceSet.getName() + "-artifacts", "1.0");
+            featureSpec.capability(project.getGroup().toString(), project.getName() + "-" + sourceSet.getName() + "-artifacts", "1.0");
             // This feature is only used internally in the
             // elasticsearch build so we do not need any publication.
             featureSpec.disablePublication();

build.gradle

@@ -95,7 +95,7 @@ tasks.named('zipAggregation').configure {
 ext.testArtifact = { p, String name = "test" ->
   def projectDependency = p.dependencies.create(p)
   projectDependency.capabilities {
-    requireCapabilities("org.elasticsearch.gradle:${projectDependency.name}-${name}-artifacts")
+    requireCapabilities("${p.group}:${projectDependency.name}-${name}-artifacts")
   };
 }
 

test/external-modules/esql-heap-attack/build.gradle

@@ -11,8 +11,6 @@ apply plugin: 'elasticsearch.internal-java-rest-test'
 // Necessary to use tests in Serverless
 apply plugin: 'elasticsearch.internal-test-artifact'
 
-group = 'org.elasticsearch.plugin'
-
 esplugin {
   description = 'A test module that can trigger out of memory'
   classname ='org.elasticsearch.test.esql.heap_attack.HeapAttackPlugin'