add workaround for test fixtures issue (#490)

* add workaround for test fixtures issue

* call get on properties because I expected more Gradle magic than there is

* unused import

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

@@ -23,9 +23,9 @@ abstract class MavenPublishBaseExtension(
 
   private val sonatypeHost: Property<SonatypeHost> = project.objects.property(SonatypeHost::class.java)
   private val signing: Property<Boolean> = project.objects.property(Boolean::class.java)
-  private val groupId: Property<String> = project.objects.property(String::class.java)
+  internal val groupId: Property<String> = project.objects.property(String::class.java)
     .convention(project.provider { project.group.toString() })
-  private val version: Property<String> = project.objects.property(String::class.java)
+  internal val version: Property<String> = project.objects.property(String::class.java)
     .convention(project.provider { project.version.toString() })
   private val pomFromProperties: Property<Boolean> = project.objects.property(Boolean::class.java)
   private val platform: Property<Platform> = project.objects.property(Platform::class.java)

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

@@ -440,6 +440,14 @@ private fun setupTestFixtures(project: Project, sourcesJar: Boolean) {
       it.suppressPomMetadataWarningsFor("testFixturesRuntimeElements")
       it.suppressPomMetadataWarningsFor("testFixturesSourcesElements")
     }
+
+    project.afterEvaluate {
+      // Gradle will put the project group and version into capabilities instead of using
+      // the publication, this can lead to invalid published metadata
+      // TODO remove after https://github.com/gradle/gradle/issues/23354 is resolved
+      project.group = project.baseExtension.groupId.get()
+      project.version = project.baseExtension.version.get()
+    }
   }
 }