temporalio · Evanthx · Mar 30, 2026 · Mar 18, 2026 · Mar 19, 2026 · Mar 23, 2026
diff --git a/core/src/main/java/io/temporal/samples/nexus/handler/EchoHandler.java b/core/src/main/java/io/temporal/samples/nexus/handler/EchoHandler.java
@@ -0,0 +1,7 @@
+package io.temporal.samples.nexus.handler;
+
+import io.temporal.samples.nexus.service.NexusService;
+
+public interface EchoHandler {
+  NexusService.EchoOutput echo(NexusService.EchoInput input);
+}
diff --git a/core/src/main/java/io/temporal/samples/nexus/handler/EchoHandlerImpl.java b/core/src/main/java/io/temporal/samples/nexus/handler/EchoHandlerImpl.java
@@ -0,0 +1,12 @@
+package io.temporal.samples.nexus.handler;
+
+import io.temporal.samples.nexus.service.NexusService;
+
+// Note that this is a class, not a Temporal worker. This is to demonstrate that Nexus services can
+// simply call a class instead of a worker for fast operations that don't need retry handling.
+public class EchoHandlerImpl implements EchoHandler {
+  @Override
+  public NexusService.EchoOutput echo(NexusService.EchoInput input) {
+    return new NexusService.EchoOutput(input.getMessage());
+  }
+}
@@ -13,16 +13,32 @@
 // return OperationHandler that correspond to the operations defined in the service interface.
 @ServiceImpl(service = NexusService.class)
 public class NexusServiceImpl {
+  private final EchoHandler echoHandler;
+
+  // The injected EchoHandler makes this class unit-testable.
+  // The no-arg constructor provides a default; the second allows tests to inject a mock.
+  // If you are not using the sync call or do not need to mock a handler, then you will not
+  // need this constructor pairing.
+  public NexusServiceImpl() {
+    this(new EchoHandlerImpl());
+  }
+
+  public NexusServiceImpl(EchoHandler echoHandler) {
+    this.echoHandler = echoHandler;
+  }
+
+  // The Echo Nexus Service exemplifies making a synchronous call using OperationHandler.sync.
+  // In this case, it is calling the EchoHandler class - not a workflow - and simply returning the
+  // result.
   @OperationImpl
   public OperationHandler<NexusService.EchoInput, NexusService.EchoOutput> echo() {
-    // OperationHandler.sync is a meant for exposing simple RPC handlers.
     return OperationHandler.sync(
         // The method is for making arbitrary short calls to other services or databases, or
         // perform simple computations such as this one. Users can also access a workflow client by
         // calling
         // Nexus.getOperationContext().getWorkflowClient(ctx) to make arbitrary calls such as
         // signaling, querying, or listing workflows.
-        (ctx, details, input) -> new NexusService.EchoOutput(input.getMessage()));
+        (ctx, details, input) -> echoHandler.echo(input));
   }
 
   @OperationImpl
@@ -39,10 +55,8 @@ public OperationHandler<NexusService.HelloInput, NexusService.HelloOutput> hello
                     .newWorkflowStub(
                         HelloHandlerWorkflow.class,
                         // Workflow IDs should typically be business meaningful IDs and are used to
-                        // dedupe workflow starts.
-                        // For this example, we're using the request ID allocated by Temporal when
-                        // the
-                        // caller workflow schedules
+                        // dedupe workflow starts. For this example, we're using the request ID
+                        // allocated by Temporal when the caller workflow schedules
                         // the operation, this ID is guaranteed to be stable across retries of this
                         // operation.
                         //

@@ -0,0 +1,76 @@
+package io.temporal.samples.nexus.caller;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.*;
+
+import io.temporal.samples.nexus.handler.EchoHandler;
+import io.temporal.samples.nexus.handler.HelloHandlerWorkflow;
+import io.temporal.samples.nexus.handler.NexusServiceImpl;
+import io.temporal.samples.nexus.service.NexusService;
+import io.temporal.testing.TestWorkflowEnvironment;
+import io.temporal.testing.TestWorkflowExtension;
+import io.temporal.worker.Worker;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+public class CallerWorkflowJunit5MockTest {
+
+  // Sync Nexus operations run inline in the handler thread — there is no backing workflow to
+  // register a factory for. To mock one, inject a mock dependency into the service implementation.
+  private static final EchoHandler mockEchoHandler = mock(EchoHandler.class);
+
+  @RegisterExtension
+  public static final TestWorkflowExtension testWorkflowExtension =
+      TestWorkflowExtension.newBuilder()
+          // If a Nexus service is registered as part of the test as in the following line of code,
+          // the TestWorkflowExtension will, by default, automatically create a Nexus service
+          // endpoint and workflows registered as part of the TestWorkflowExtension will
+          // automatically inherit the endpoint if none is set.
+          .setNexusServiceImplementation(new NexusServiceImpl(mockEchoHandler))
+          // The Echo Nexus handler service just makes a call to a class, so no extra setup is
+          // needed. But the Hello Nexus service needs a worker for both the caller and handler
+          // in order to run, and the Echo Nexus caller service needs a worker.
+          //
+          // registerWorkflowImplementationTypes will take the classes given and create workers for
+          // them, enabling workflows to run.
+          .registerWorkflowImplementationTypes(
+              HelloCallerWorkflowImpl.class, EchoCallerWorkflowImpl.class)
+          .setDoNotStart(true)
+          .build();
+
+  @Test
+  public void testHelloWorkflow(
+      TestWorkflowEnvironment testEnv, Worker worker, HelloCallerWorkflow workflow) {
+    // Workflows started by a Nexus service can be mocked just like any other workflow
+    worker.registerWorkflowImplementationFactory(
+        HelloHandlerWorkflow.class,
+        () -> {
+          HelloHandlerWorkflow mockHandler = mock(HelloHandlerWorkflow.class);
+          when(mockHandler.hello(any()))
+              .thenReturn(new NexusService.HelloOutput("Hello Mock World 👋"));
+          return mockHandler;
+        });
+    testEnv.start();
+
+    // Execute a workflow waiting for it to complete.
+    String greeting = workflow.hello("World", NexusService.Language.EN);
+    assertEquals("Hello Mock World 👋", greeting);
+
+    testEnv.shutdown();
+  }
+
+  @Test
+  public void testEchoWorkflow(
+      TestWorkflowEnvironment testEnv, Worker worker, EchoCallerWorkflow workflow) {
+    // Sync Nexus operations run inline in the handler thread — there is no backing workflow to
+    // register a factory for. Instead, stub the injected EchoHandler dependency directly.
+    when(mockEchoHandler.echo(any())).thenReturn(new NexusService.EchoOutput("mocked echo"));
+    testEnv.start();
+
+    // Execute a workflow waiting for it to complete.
+    String greeting = workflow.echo("Hello");
+    assertEquals("mocked echo", greeting);
+
+    testEnv.shutdown();
+  }
+}
@@ -0,0 +1,55 @@
+package io.temporal.samples.nexus.caller;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import io.temporal.samples.nexus.handler.HelloHandlerWorkflowImpl;
+import io.temporal.samples.nexus.handler.NexusServiceImpl;
+import io.temporal.samples.nexus.service.NexusService;
+import io.temporal.testing.TestWorkflowEnvironment;
+import io.temporal.testing.TestWorkflowExtension;
+import io.temporal.worker.Worker;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+public class CallerWorkflowJunit5Test {
+
+  @RegisterExtension
+  public static final TestWorkflowExtension testWorkflowExtension =
+      TestWorkflowExtension.newBuilder()
+          // If a Nexus service is registered as part of the test as in the following line of code,
+          // the TestWorkflowExtension will, by default, automatically create a Nexus service
+          // endpoint and workflows registered as part of the TestWorkflowExtension will
+          // automatically inherit the endpoint if none is set.
+          .setNexusServiceImplementation(new NexusServiceImpl())
+          // The Echo Nexus handler service just makes a call to a class, so no extra setup is
+          // needed. But the Hello Nexus service needs a worker for both the caller and handler
+          // in order to run, and the Echo Nexus caller service needs a worker.
+          //
+          // registerWorkflowImplementationTypes will take the classes given and create workers for
+          // them, enabling workflows to run.
+          .registerWorkflowImplementationTypes(
+              HelloCallerWorkflowImpl.class,
+              HelloHandlerWorkflowImpl.class,
+              EchoCallerWorkflowImpl.class)
+          // The workflow will start before each test, and will shut down after each test.
+          // See CallerWorkflowTest for an example of how to control this differently if needed.
+          .build();
+
+  // The TestWorkflowExtension extension in the Temporal testing library creates the
+  // arguments to the test cases and initializes them from the extension setup call above.
+  @Test
+  public void testHelloWorkflow(
+      TestWorkflowEnvironment testEnv, Worker worker, HelloCallerWorkflow workflow) {
+    // Execute a workflow waiting for it to complete.
+    String greeting = workflow.hello("World", NexusService.Language.EN);
+    assertEquals("Hello World 👋", greeting);
+  }
+
+  @Test
+  public void testEchoWorkflow(
+      TestWorkflowEnvironment testEnv, Worker worker, EchoCallerWorkflow workflow) {
+    // Execute a workflow waiting for it to complete.
+    String greeting = workflow.echo("Hello");
+    assertEquals("Hello", greeting);
+  }
+}
@@ -0,0 +1,88 @@
+package io.temporal.samples.nexus.caller;
+
+import static org.junit.Assert.assertEquals;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import io.temporal.client.WorkflowOptions;
+import io.temporal.samples.nexus.handler.EchoHandler;
+import io.temporal.samples.nexus.handler.HelloHandlerWorkflow;
+import io.temporal.samples.nexus.handler.NexusServiceImpl;
+import io.temporal.samples.nexus.service.NexusService;
+import io.temporal.testing.TestWorkflowRule;
+import org.junit.Rule;
+import org.junit.Test;
+
+public class CallerWorkflowMockTest {
+
+  // Inject a mock EchoHandler so sync Nexus operations can be stubbed per test.
+  // JUnit 4 creates a new test class instance per test method, so this mock is fresh each time.
+  private final EchoHandler mockEchoHandler = mock(EchoHandler.class);
+
+  @Rule
+  public TestWorkflowRule testWorkflowRule =
+      TestWorkflowRule.newBuilder()
+          // If a Nexus service is registered as part of the test as in the following line of code,
+          // the TestWorkflowRule will, by default, automatically create a Nexus service endpoint
+          // and workflows registered as part of the TestWorkflowRule
+          // will automatically inherit the endpoint if none is set.
+          .setNexusServiceImplementation(new NexusServiceImpl(mockEchoHandler))
+          // The Echo Nexus handler service just makes a call to a class, so no extra setup is
+          // needed. But the Hello Nexus service needs a worker for both the caller and handler
+          // in order to run.
+          // setWorkflowTypes will take the classes given and create workers for them, enabling
+          // workflows to run. This creates caller workflows, the handler workflows
+          // will be mocked in the test methods.
+          .setWorkflowTypes(HelloCallerWorkflowImpl.class, EchoCallerWorkflowImpl.class)
+          // Disable automatic worker startup as we are going to register some workflows manually
+          // per test
+          .setDoNotStart(true)
+          .build();
+
+  @Test
+  public void testHelloWorkflow() {
+    testWorkflowRule
+        .getWorker()
+        // Workflows started by a Nexus service can be mocked just like any other workflow
+        .registerWorkflowImplementationFactory(
+            HelloHandlerWorkflow.class,
+            () -> {
+              HelloHandlerWorkflow wf = mock(HelloHandlerWorkflow.class);
+              when(wf.hello(any())).thenReturn(new NexusService.HelloOutput("Hello Mock World 👋"));
+              return wf;
+            });
+    testWorkflowRule.getTestEnvironment().start();
+
+    // Now create the caller workflow
+    HelloCallerWorkflow workflow =
+        testWorkflowRule
+            .getWorkflowClient()
+            .newWorkflowStub(
+                HelloCallerWorkflow.class,
+                WorkflowOptions.newBuilder().setTaskQueue(testWorkflowRule.getTaskQueue()).build());
+    String greeting = workflow.hello("World", NexusService.Language.EN);
+    assertEquals("Hello Mock World 👋", greeting);
+
+    testWorkflowRule.getTestEnvironment().shutdown();
+  }
+
+  @Test
+  public void testEchoWorkflow() {
+    // Sync Nexus operations run inline in the handler thread — there is no backing workflow to
+    // register a factory for. Instead, stub the injected EchoHandler dependency directly.
+    when(mockEchoHandler.echo(any())).thenReturn(new NexusService.EchoOutput("mocked echo"));
+    testWorkflowRule.getTestEnvironment().start();
+
+    EchoCallerWorkflow workflow =
+        testWorkflowRule
+            .getWorkflowClient()
+            .newWorkflowStub(
+                EchoCallerWorkflow.class,
+                WorkflowOptions.newBuilder().setTaskQueue(testWorkflowRule.getTaskQueue()).build());
+    String greeting = workflow.echo("Hello");
+    assertEquals("mocked echo", greeting);
+
+    testWorkflowRule.getTestEnvironment().shutdown();
+  }
+}
@@ -1,12 +1,9 @@
 package io.temporal.samples.nexus.caller;
 
 import static org.junit.Assert.assertEquals;
-import static org.mockito.ArgumentMatchers.any;
-import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.when;
 
 import io.temporal.client.WorkflowOptions;
-import io.temporal.samples.nexus.handler.HelloHandlerWorkflow;
+import io.temporal.samples.nexus.handler.HelloHandlerWorkflowImpl;
 import io.temporal.samples.nexus.handler.NexusServiceImpl;
 import io.temporal.samples.nexus.service.NexusService;
 import io.temporal.testing.TestWorkflowRule;
@@ -21,28 +18,26 @@ public class CallerWorkflowTest {
   @Rule
   public TestWorkflowRule testWorkflowRule =
       TestWorkflowRule.newBuilder()
-          // If a Nexus service is registered as part of the test, the TestWorkflowRule will ,by
-          // default, automatically create a Nexus service endpoint and workflows registered as part
-          // of the TestWorkflowRule will automatically inherit the endpoint if none is set.
+          // If a Nexus service is registered as part of the test as in the following line of code,
+          // the TestWorkflowRule will, by default, automatically create a Nexus service endpoint
+          // and workflows registered as part of the TestWorkflowRule
+          // will automatically inherit the endpoint if none is set.
           .setNexusServiceImplementation(new NexusServiceImpl())
-          .setWorkflowTypes(HelloCallerWorkflowImpl.class)
+          // The Echo Nexus handler service just makes a call to a class, so no extra setup is
+          // needed. But the Hello Nexus service needs a worker for both the caller and handler
+          // in order to run.
+          // setWorkflowTypes will take the classes given and create workers for them, enabling
+          // workflows to run. This is not adding an EchoCallerWorkflow though -
+          // see the testEchoWorkflow test method below for an example of an alternate way
+          // to supply a worker that gives you more flexibility if needed.
+          .setWorkflowTypes(HelloCallerWorkflowImpl.class, HelloHandlerWorkflowImpl.class)
           // Disable automatic worker startup as we are going to register some workflows manually
           // per test
           .setDoNotStart(true)
           .build();
 
   @Test
   public void testHelloWorkflow() {
-    testWorkflowRule
-        .getWorker()
-        // Workflows started by a Nexus service can be mocked just like any other workflow
-        .registerWorkflowImplementationFactory(
-            HelloHandlerWorkflow.class,
-            () -> {
-              HelloHandlerWorkflow wf = mock(HelloHandlerWorkflow.class);
-              when(wf.hello(any())).thenReturn(new NexusService.HelloOutput("Hello World 👋"));
-              return wf;
-            });
     testWorkflowRule.getTestEnvironment().start();
 
     HelloCallerWorkflow workflow =
@@ -61,8 +56,13 @@ public void testHelloWorkflow() {
   public void testEchoWorkflow() {
     // If Workflows are registered later than the endpoint can be set manually
     // either by setting the endpoint in the NexusServiceOptions in the Workflow implementation or
-    // by setting the NexusServiceOptions on the WorkflowImplementationOptions when registering the
-    // Workflow.
+    // by setting the NexusServiceOptions on the WorkflowImplementationOptions when registering
+    // the Workflow. To demonstrate, this is creating the Nexus service for Echo,
+    // and registering a EchoCallerWorkflowImpl worker.
+    //
+    // It is much simpler to use the setWorkflowTypes in the rule definition above - and as
+    // this isn't easily do-able in JUnit5 (the nexus endpoint isn't exposed) should be
+    // used with caution.
     testWorkflowRule
         .getWorker()
         .registerWorkflowImplementationTypes(