Add unit tests for DurableTaskGrpcClientFactory (#257)

* Initial plan

* Add unit tests for DurableTaskGrpcClientFactory and fix compilation error

Co-authored-by: sophiatev <38052607+sophiatev@users.noreply.github.com>

* Remove changes to DurableTaskGrpcClient.java and proto file, keep only test file

Co-authored-by: sophiatev <38052607+sophiatev@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: sophiatev <38052607+sophiatev@users.noreply.github.com>

Author: Copilot

client/src/test/java/com/microsoft/durabletask/DurableTaskGrpcClientFactoryTest.java

@@ -0,0 +1,74 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package com.microsoft.durabletask;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Unit tests for DurableTaskGrpcClientFactory.
+ */
+public class DurableTaskGrpcClientFactoryTest {
+
+    @Test
+    void getClient_samePort_returnsSameInstance() {
+        // Arrange
+        int port = 5001;
+
+        // Act
+        DurableTaskClient client1 = DurableTaskGrpcClientFactory.getClient(port);
+        DurableTaskClient client2 = DurableTaskGrpcClientFactory.getClient(port);
+
+        // Assert
+        assertNotNull(client1, "First client should not be null");
+        assertNotNull(client2, "Second client should not be null");
+        assertSame(client1, client2, "getClient should return the same instance for the same port");
+    }
+
+    @Test
+    void getClient_differentPorts_returnsDifferentInstances() {
+        // Arrange
+        int port1 = 5002;
+        int port2 = 5003;
+
+        // Act
+        DurableTaskClient client1 = DurableTaskGrpcClientFactory.getClient(port1);
+        DurableTaskClient client2 = DurableTaskGrpcClientFactory.getClient(port2);
+
+        // Assert
+        assertNotNull(client1, "Client for port1 should not be null");
+        assertNotNull(client2, "Client for port2 should not be null");
+        assertNotSame(client1, client2, "getClient should return different instances for different ports");
+    }
+
+    @Test
+    void getClient_multiplePorts_maintainsCorrectMapping() {
+        // Arrange
+        int port1 = 5004;
+        int port2 = 5005;
+        int port3 = 5006;
+
+        // Act
+        DurableTaskClient client1 = DurableTaskGrpcClientFactory.getClient(port1);
+        DurableTaskClient client2 = DurableTaskGrpcClientFactory.getClient(port2);
+        DurableTaskClient client3 = DurableTaskGrpcClientFactory.getClient(port3);
+        
+        // Request the same ports again
+        DurableTaskClient client1Again = DurableTaskGrpcClientFactory.getClient(port1);
+        DurableTaskClient client2Again = DurableTaskGrpcClientFactory.getClient(port2);
+        DurableTaskClient client3Again = DurableTaskGrpcClientFactory.getClient(port3);
+
+        // Assert
+        // Verify each port returns the same instance
+        assertSame(client1, client1Again, "Port " + port1 + " should return the same instance");
+        assertSame(client2, client2Again, "Port " + port2 + " should return the same instance");
+        assertSame(client3, client3Again, "Port " + port3 + " should return the same instance");
+        
+        // Verify all instances are different from each other
+        assertNotSame(client1, client2, "Client for port1 and port2 should be different");
+        assertNotSame(client1, client3, "Client for port1 and port3 should be different");
+        assertNotSame(client2, client3, "Client for port2 and port3 should be different");
+    }
+}