diff --git a/flytekit-testing/src/main/java/org/flyte/flytekit/testing/SdkTestingExecutor.java b/flytekit-testing/src/main/java/org/flyte/flytekit/testing/SdkTestingExecutor.java
index 17e5f8be2..981949152 100644
--- a/flytekit-testing/src/main/java/org/flyte/flytekit/testing/SdkTestingExecutor.java
+++ b/flytekit-testing/src/main/java/org/flyte/flytekit/testing/SdkTestingExecutor.java
@@ -401,15 +401,17 @@ public <InputT, OutputT> SdkTestingExecutor withWorkflowOutput(
 
     // fixed tasks
     TestingRunnableTask<InputT, OutputT> fixedTask =
-        getFixedTaskOrDefault(workflow.getName(), inputType, outputType);
+        getFixedTaskOrDefault(workflow.getName(), inputType, outputType)
+            .withFixedOutput(input, output);
 
     // replace workflow
     SdkWorkflow<InputT, OutputT> mockWorkflow =
-        new TestingWorkflow<>(inputType, outputType, output);
+        new TestingWorkflow<>(inputType, outputType, fixedTask.fixedOutputs);
 
     return toBuilder()
         .putWorkflowTemplate(workflow.getName(), mockWorkflow.toIdlTemplate())
-        .putFixedTask(workflow.getName(), fixedTask.withFixedOutput(input, output))
+        .putFixedTask(workflow.getName(), fixedTask)
+        .putFixedTask(TestingWorkflow.TestingSdkRunnableTask.class.getName(), fixedTask)
         .build();
   }
 
diff --git a/flytekit-testing/src/main/java/org/flyte/flytekit/testing/TestingWorkflow.java b/flytekit-testing/src/main/java/org/flyte/flytekit/testing/TestingWorkflow.java
index 0339fb180..f5b2bd5fc 100644
--- a/flytekit-testing/src/main/java/org/flyte/flytekit/testing/TestingWorkflow.java
+++ b/flytekit-testing/src/main/java/org/flyte/flytekit/testing/TestingWorkflow.java
@@ -16,6 +16,8 @@
  */
 package org.flyte.flytekit.testing;
 
+import java.util.Map;
+import org.flyte.flytekit.SdkRunnableTask;
 import org.flyte.flytekit.SdkType;
 import org.flyte.flytekit.SdkWorkflow;
 import org.flyte.flytekit.SdkWorkflowBuilder;
@@ -23,15 +25,36 @@
 /** {@link SdkWorkflow} that can fix output for specific input. */
 class TestingWorkflow<InputT, OutputT> extends SdkWorkflow<InputT, OutputT> {
 
-  private final OutputT output;
+  private final Map<InputT, OutputT> outputs;
 
-  TestingWorkflow(SdkType<InputT> inputType, SdkType<OutputT> outputType, OutputT output) {
+  TestingWorkflow(
+      SdkType<InputT> inputType, SdkType<OutputT> outputType, Map<InputT, OutputT> outputs) {
     super(inputType, outputType);
-    this.output = output;
+    this.outputs = outputs;
   }
 
   @Override
   public OutputT expand(SdkWorkflowBuilder builder, InputT input) {
-    return output;
+    return builder
+        .apply(new TestingSdkRunnableTask<>(getInputType(), getOutputType(), outputs), input)
+        .getOutputs();
+  }
+
+  public static class TestingSdkRunnableTask<InputT, OutputT>
+      extends SdkRunnableTask<InputT, OutputT> {
+    private static final long serialVersionUID = 6106269076155338045L;
+
+    private final Map<InputT, OutputT> outputs;
+
+    public TestingSdkRunnableTask(
+        SdkType<InputT> inputType, SdkType<OutputT> outputType, Map<InputT, OutputT> outputs) {
+      super(inputType, outputType);
+      this.outputs = outputs;
+    }
+
+    @Override
+    public OutputT run(InputT input) {
+      return outputs.get(input);
+    }
   }
 }
diff --git a/flytekit-testing/src/test/java/org/flyte/flytekit/testing/MockSubWorkflowsTest.java b/flytekit-testing/src/test/java/org/flyte/flytekit/testing/MockSubWorkflowsTest.java
new file mode 100644
index 000000000..6e96ea2a7
--- /dev/null
+++ b/flytekit-testing/src/test/java/org/flyte/flytekit/testing/MockSubWorkflowsTest.java
@@ -0,0 +1,107 @@
+/*
+ * Copyright 2024 Flyte Authors.
+ *
+ * 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.flyte.flytekit.testing;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.equalTo;
+
+import com.google.auto.value.AutoValue;
+import org.flyte.flytekit.SdkBindingData;
+import org.flyte.flytekit.SdkBindingDataFactory;
+import org.flyte.flytekit.SdkWorkflow;
+import org.flyte.flytekit.SdkWorkflowBuilder;
+import org.flyte.flytekit.jackson.JacksonSdkType;
+import org.junit.jupiter.api.Test;
+
+public class MockSubWorkflowsTest {
+  @Test
+  public void test() {
+    SdkTestingExecutor.Result result =
+        SdkTestingExecutor.of(new Workflow())
+            .withFixedInputs(
+                JacksonSdkType.of(SubWorkflowInputs.class),
+                SubWorkflowInputs.create(SdkBindingDataFactory.of(1)))
+            .withWorkflowOutput(
+                new SubWorkflow(),
+                JacksonSdkType.of(SubWorkflowInputs.class),
+                SubWorkflowInputs.create(SdkBindingDataFactory.of(1)),
+                JacksonSdkType.of(SubWorkflowOutputs.class),
+                SubWorkflowOutputs.create(SdkBindingDataFactory.of(10)))
+            .withWorkflowOutput(
+                new SubWorkflow(),
+                JacksonSdkType.of(SubWorkflowInputs.class),
+                SubWorkflowInputs.create(SdkBindingDataFactory.of(2)),
+                JacksonSdkType.of(SubWorkflowOutputs.class),
+                SubWorkflowOutputs.create(SdkBindingDataFactory.of(20)))
+            .execute();
+
+    assertThat(result.getIntegerOutput("o"), equalTo(10L));
+  }
+
+  public static class Workflow extends SdkWorkflow<SubWorkflowInputs, SubWorkflowOutputs> {
+    public Workflow() {
+      super(
+          JacksonSdkType.of(SubWorkflowInputs.class), JacksonSdkType.of(SubWorkflowOutputs.class));
+    }
+
+    @Override
+    public SubWorkflowOutputs expand(SdkWorkflowBuilder builder, SubWorkflowInputs inputs) {
+
+      var subOut1 =
+          builder
+              .apply(
+                  "sub", new SubWorkflow(), SubWorkflowInputs.create(SdkBindingDataFactory.of(1)))
+              .getOutputs();
+      builder
+          .apply("sub1", new SubWorkflow(), SubWorkflowInputs.create(SdkBindingDataFactory.of(2)))
+          .getOutputs();
+
+      return SubWorkflowOutputs.create(subOut1.o());
+    }
+  }
+
+  public static class SubWorkflow extends SdkWorkflow<SubWorkflowInputs, SubWorkflowOutputs> {
+    public SubWorkflow() {
+      super(
+          JacksonSdkType.of(SubWorkflowInputs.class), JacksonSdkType.of(SubWorkflowOutputs.class));
+    }
+
+    @Override
+    public SubWorkflowOutputs expand(SdkWorkflowBuilder builder, SubWorkflowInputs inputs) {
+
+      return SubWorkflowOutputs.create(inputs.a());
+    }
+  }
+
+  @AutoValue
+  public abstract static class SubWorkflowInputs {
+    public abstract SdkBindingData<Long> a();
+
+    public static MockSubWorkflowsTest.SubWorkflowInputs create(SdkBindingData<Long> a) {
+      return new AutoValue_MockSubWorkflowsTest_SubWorkflowInputs(a);
+    }
+  }
+
+  @AutoValue
+  public abstract static class SubWorkflowOutputs {
+    public abstract SdkBindingData<Long> o();
+
+    public static MockSubWorkflowsTest.SubWorkflowOutputs create(SdkBindingData<Long> o) {
+      return new AutoValue_MockSubWorkflowsTest_SubWorkflowOutputs(o);
+    }
+  }
+}