Metamorph tests verify that no unexpected interactions occurred (first batch).

metamorph/build.gradle

@@ -39,3 +39,10 @@ sourceSets {
     output.resourcesDir = sourceSets.test.java.outputDir
   }
 }
+
+test {
+  testLogging {
+    showStandardStreams = true
+    exceptionFormat = 'full'
+  }
+}

metamorph/src/test/java/org/metafacture/metamorph/TestHelpers.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2020 hbz NRW
+ *
+ * Licensed under the Apache License, Version 2.0 the "License";
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.metafacture.metamorph;
+
+import org.metafacture.framework.StreamReceiver;
+import org.mockito.InOrder;
+import org.mockito.Mockito;
+import org.mockito.exceptions.base.MockitoAssertionError;
+
+import java.util.function.BiConsumer;
+import java.util.function.Consumer;
+import java.util.function.IntFunction;
+import java.util.function.Supplier;
+
+/**
+ * Helper functions for Metamorph tests.
+ *
+ * @author Jens Wille
+ */
+public final class TestHelpers {
+
+    public static void assertMorph(final StreamReceiver receiver, final String morphDef, final Consumer<Metamorph> in, final Consumer<Supplier<StreamReceiver>> out) {
+        assertMorph(receiver, morphDef, in, (s, f) -> out.accept(s));
+    }
+
+    public static void assertMorph(final StreamReceiver receiver, final String morphDef, final Consumer<Metamorph> in, final BiConsumer<Supplier<StreamReceiver>, IntFunction<StreamReceiver>> out) {
+        final Metamorph metamorph = InlineMorph.in(TestHelpers.class).with(morphDef).createConnectedTo(receiver);
+        final InOrder ordered = Mockito.inOrder(receiver);
+
+        try {
+            in.accept(metamorph);
+            out.accept(() -> ordered.verify(receiver), i -> ordered.verify(receiver, Mockito.times(i)));
+
+            ordered.verifyNoMoreInteractions();
+            Mockito.verifyNoMoreInteractions(receiver);
+        }
+        catch (final MockitoAssertionError e) {
+            System.out.println(Mockito.mockingDetails(receiver).printInvocations());
+            throw e;
+        }
+    }
+
+}