also setup test fixtures sources jar for Kotlin/JVM, suppress warnings

plugin/src/integrationTest/fixtures2/src/testFixtures/kotlin/com/vanniktech/maven/publish/test/TestFixtureKotlinClass.kt

@@ -0,0 +1,6 @@
+package com.vanniktech.maven.publish.test
+
+/**
+ * Just a test fixture class in Kotlin.
+ */
+public class TestFixtureKotlinClass

plugin/src/integrationTest/kotlin/com/vanniktech/maven/publish/MavenPublishPluginPlatformTest.kt

@@ -76,7 +76,10 @@ class MavenPublishPluginPlatformTest {
     assertThat(result).artifact("jar").isSigned()
     assertThat(result).pom().exists()
     assertThat(result).pom().isSigned()
-    assertThat(result).pom().matchesExpectedPom(PomDependency("com.example", "test-artifact", "1.0.0", "compile", true))
+    assertThat(result).pom().matchesExpectedPom(
+      // TODO: Gradle currently adds a self dependency when test fixtures are published https://github.com/gradle/gradle/issues/14936
+      PomDependency("com.example", "test-artifact", "1.0.0", "compile", true),
+    )
     assertThat(result).module().exists()
     assertThat(result).module().isSigned()
     assertThat(result).sourcesJar().exists()
@@ -169,6 +172,42 @@ class MavenPublishPluginPlatformTest {
     assertThat(result).javadocJar().isSigned()
   }
 
+  @TestParameterInjectorTest
+  fun kotlinJvmWithTestFixturesProject(@TestParameter kotlinVersion: KotlinVersion) {
+    val default = kotlinJvmProjectSpec(kotlinVersion)
+    val project = default.copy(
+      plugins = default.plugins + javaTestFixturesPlugin,
+      sourceFiles = default.sourceFiles + listOf(
+        SourceFile("testFixtures", "java", "com/vanniktech/maven/publish/test/TestFixtureClass.java"),
+        SourceFile("testFixtures", "kotlin", "com/vanniktech/maven/publish/test/TestFixtureKotlinClass.kt"),
+      )
+    )
+    val result = project.run(fixtures, testProjectDir, testOptions)
+
+    assertThat(result).outcome().succeeded()
+    assertThat(result).artifact("jar").exists()
+    assertThat(result).artifact("jar").isSigned()
+    assertThat(result).pom().exists()
+    assertThat(result).pom().isSigned()
+    assertThat(result).pom().matchesExpectedPom(
+      kotlinStdlibJdk(kotlinVersion),
+      // TODO: Gradle currently adds a self dependency when test fixtures are published https://github.com/gradle/gradle/issues/14936
+      PomDependency("com.example", "test-artifact", "1.0.0", "compile", true),
+    )
+    assertThat(result).module().exists()
+    assertThat(result).module().isSigned()
+    assertThat(result).sourcesJar().exists()
+    assertThat(result).sourcesJar().isSigned()
+    assertThat(result).sourcesJar().containsSourceSetFiles("main")
+    assertThat(result).javadocJar().exists()
+    assertThat(result).javadocJar().isSigned()
+    assertThat(result).artifact("test-fixtures", "jar").exists()
+    assertThat(result).artifact("test-fixtures", "jar").isSigned()
+    assertThat(result).sourcesJar("test-fixtures").exists()
+    assertThat(result).sourcesJar("test-fixtures").isSigned()
+    assertThat(result).sourcesJar("test-fixtures").containsSourceSetFiles("testFixtures")
+  }
+
   @TestParameterInjectorTest
   fun kotlinJsProject(@TestParameter kotlinVersion: KotlinVersion) {
     val project = kotlinJsProjectSpec(kotlinVersion)

plugin/src/main/kotlin/com/vanniktech/maven/publish/Platform.kt

@@ -57,14 +57,7 @@ data class JavaLibrary @JvmOverloads constructor(
       it.withJavadocJar { project.javadocJarTask(javadocJar) }
     }
 
-    if (sourcesJar) {
-      // TODO: remove after https://github.com/gradle/gradle/issues/20539 is resolved
-      project.plugins.withId("java-test-fixtures") {
-        project.serviceOf<JvmModelingServices>().createJvmVariant("testFixtures") {
-          it.withSourcesJar().published()
-        }
-      }
-    }
+    setupTestFixtures(project, sourcesJar)
   }
 }
 
@@ -278,6 +271,8 @@ data class KotlinJvm @JvmOverloads constructor(
       it.withSourcesJar { project.javaSourcesJar(sourcesJar) }
       it.withJavadocJar { project.javadocJarTask(javadocJar) }
     }
+
+    setupTestFixtures(project, sourcesJar)
   }
 }
 
@@ -430,6 +425,25 @@ private fun MavenPublication.withJavadocJar(factory: () -> TaskProvider<*>?) {
   }
 }
 
+private fun setupTestFixtures(project: Project, sourcesJar: Boolean) {
+  project.plugins.withId("java-test-fixtures") {
+    if (sourcesJar) {
+      // TODO: remove after https://github.com/gradle/gradle/issues/20539 is resolved
+      project.serviceOf<JvmModelingServices>().createJvmVariant("testFixtures") {
+        it.withSourcesJar().published()
+      }
+    }
+
+    // test fixtures can't be mapped to the POM because there is no equivalent concept in Maven
+    project.mavenPublications {
+      it.suppressPomMetadataWarningsFor("testFixturesApiElements")
+      it.suppressPomMetadataWarningsFor("testFixturesRuntimeElements")
+      it.suppressPomMetadataWarningsFor("testFixturesSourcesElements")
+
+    }
+  }
+}
+
 private class MissingVariantException(name: String) : RuntimeException(
   "Invalid MavenPublish Configuration. Unable to find variant to publish named $name." +
     " Try setting the 'androidVariantToPublish' property in the mavenPublish" +