test: fix unfinished stubbing of command response writer

The engine is shared across multiple tests and not stopped in-between.
With this change we only set up mocking of the response writer once and
not for every test method. This ensures that mocking does not interfere
with engine processing from previous tests which would show up as
unfinished mocking exceptions.

While both versions of `interceptResponseWriter` should be equivalent,
the previous version would sometimes fail with an
`UnfinishedStubbingException`.

engine/src/test/java/io/camunda/zeebe/engine/processing/processinstance/CreateProcessInstanceWithResultTest.java

@@ -41,21 +41,25 @@ public final class CreateProcessInstanceWithResultTest {
   public final RecordingExporterTestWatcher recordingExporterTestWatcher =
       new RecordingExporterTestWatcher();
 
-  private ProcessInstanceResultRecord response;
-  private CommandResponseWriter mockCommandResponseWriter;
+  private static ProcessInstanceResultRecord response;
+  private static CommandResponseWriter mockCommandResponseWriter;
 
   @BeforeClass
   public static void init() {
     ENGINE.deployment().withXmlResource(PROCESS).deploy();
   }
 
-  @Before
-  public void setUp() {
+  @BeforeClass
+  public static void setUp() {
     mockCommandResponseWriter = ENGINE.getCommandResponseWriter();
-    Mockito.clearInvocations(mockCommandResponseWriter);
     interceptResponseWriter(mockCommandResponseWriter);
   }
 
+  @Before
+  public void reset() {
+    Mockito.clearInvocations(mockCommandResponseWriter);
+  }
+
   @Test
   public void shouldSendResultAfterCompletion() {
     // given
@@ -159,7 +163,8 @@ public void shouldSendRejectionImmediately() {
     verify(ENGINE.getCommandResponseWriter(), timeout(1000).times(1)).tryWriteResponse(3, 3);
   }
 
-  private void interceptResponseWriter(final CommandResponseWriter mockCommandResponseWriter) {
+  private static void interceptResponseWriter(
+      final CommandResponseWriter mockCommandResponseWriter) {
     doAnswer(
             (Answer<CommandResponseWriter>)
                 (invocation -> {