Fix exception when ClassSelectors contain interfaces (#2)

+ Avoid computing the entire class hierarchy unnecessarily

Fixes #1.

src/main/java/org/junit/support/testng/engine/TestAnnotationUtils.java

@@ -10,13 +10,16 @@
 
 package org.junit.support.testng.engine;
 
+import static java.util.Spliterators.spliteratorUnknownSize;
+
 import java.lang.reflect.Method;
-import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.List;
+import java.util.Iterator;
 import java.util.Objects;
 import java.util.Optional;
+import java.util.Spliterator;
 import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
 
 import org.testng.ITestNGMethod;
 import org.testng.annotations.Test;
@@ -74,16 +77,27 @@ static Stream<String> collectGroups(Class<?> testClass) {
 	}
 
 	private static Stream<Test> collectTestAnnotations(Class<?> testClass) {
-		return getClassHierarchy(testClass).stream() //
+		return getClassHierarchy(testClass) //
 				.map(clazz -> clazz.getAnnotation(Test.class)) //
 				.filter(Objects::nonNull);
 	}
 
-	private static List<Class<?>> getClassHierarchy(Class<?> testClass) {
-		List<Class<?>> result = new ArrayList<>();
-		for (Class<?> clazz = testClass; clazz != Object.class; clazz = clazz.getSuperclass()) {
-			result.add(clazz);
-		}
-		return result;
+	private static Stream<Class<?>> getClassHierarchy(Class<?> testClass) {
+		Iterator<Class<?>> iterator = new Iterator<Class<?>>() {
+			Class<?> next = testClass;
+
+			@Override
+			public boolean hasNext() {
+				return next != Object.class && next != null;
+			}
+
+			@Override
+			public Class<?> next() {
+				Class<?> result = next;
+				next = next.getSuperclass();
+				return result;
+			}
+		};
+		return StreamSupport.stream(spliteratorUnknownSize(iterator, Spliterator.ORDERED), false);
 	}
 }

src/test/java/org/junit/support/testng/engine/DiscoveryIntegrationTests.java

@@ -261,4 +261,27 @@ void ignoresIgnoredTests() {
 		TestDescriptor methodDescriptor = getOnlyElement(classDescriptor.getChildren());
 		assertThat(methodDescriptor.getDisplayName()).isEqualTo("test");
 	}
+
+	@ParameterizedTest
+	@ValueSource(classes = { InterfaceTestCase.class, AbstractTestCase.class, RecordTestCase.class,
+			EnumTestCase.class })
+	void doesNotThrowExceptionWhenNonExecutableTypeOfClassIsSelected(Class<?> testClass) {
+		var request = request().selectors(selectClass(testClass)).build();
+
+		var rootDescriptor = testEngine.discover(request, engineId);
+
+		assertThat(rootDescriptor.getChildren()).isEmpty();
+	}
+
+	interface InterfaceTestCase {
+	}
+
+	static abstract class AbstractTestCase {
+	}
+
+	record RecordTestCase() {
+	}
+
+	enum EnumTestCase {
+	}
 }