Fix running JUnit test method in abstract class

Previously led to running all methods in an inheritor class
Untested because behaviour is rare and we don't have test covering JUnit run configuration

 #KT-28080 Fixed

idea/idea-jvm/src/org/jetbrains/kotlin/idea/run/KotlinJUnitRunConfigurationProducer.kt

@@ -107,7 +107,8 @@ class KotlinJUnitRunConfigurationProducer : RunConfigurationProducer<JUnitConfig
 
     override fun onFirstRun(fromContext: ConfigurationFromContext, context: ConfigurationContext, performRunnable: Runnable) {
         val leaf = fromContext.sourceElement
-        val sourceElement = getTestClass(leaf) ?: return super.onFirstRun(fromContext, context, performRunnable)
+        val sourceElement =
+            getTestMethod(leaf) as? PsiMember ?: getTestClass(leaf) ?: return super.onFirstRun(fromContext, context, performRunnable)
 
         val contextWithLightElement = createDelegatingContextWithLightElement(fromContext, sourceElement)
         // TODO: use TestClassConfigurationProducer when constructor becomes public