BAEL-9625: Testing Model Context Protocol (MCP) Tools in Spring AI

spring-ai-modules/spring-ai-mcp/pom.xml

@@ -44,7 +44,7 @@
 
     <properties>
         <java.version>21</java.version>
-        <spring-ai.version>1.0.1</spring-ai.version>
+        <spring-ai.version>1.1.2</spring-ai.version>
     </properties>
 
     <profiles>

spring-ai-modules/spring-ai-mcp/src/main/java/com/baeldung/springai/mcp/test/ExchangeRateMcpTool.java

@@ -0,0 +1,22 @@
+package com.baeldung.springai.mcp.test;
+
+import org.springaicommunity.mcp.annotation.McpTool;
+import org.springaicommunity.mcp.annotation.McpToolParam;
+import org.springframework.stereotype.Component;
+
+@Component
+public class ExchangeRateMcpTool {
+
+    private final ExchangeRateService exchangeRateService;
+
+    public ExchangeRateMcpTool(ExchangeRateService exchangeRateService) {
+        this.exchangeRateService = exchangeRateService;
+    }
+
+    @McpTool(description = "Get the latest exchange rates for a base currency")
+    public ExchangeRateResponse getLatestExchangeRate(
+        @McpToolParam(description = "Base currency code, e.g. GBP, USD, EUR", required = true) String base) {
+        return exchangeRateService.getLatestExchangeRate(base);
+    }
+
+}

spring-ai-modules/spring-ai-mcp/src/main/java/com/baeldung/springai/mcp/test/ExchangeRateResponse.java

@@ -0,0 +1,6 @@
+package com.baeldung.springai.mcp.test;
+
+import java.util.Map;
+
+public record ExchangeRateResponse(double amount, String base, String date, Map<String, Double> rates) {
+}

spring-ai-modules/spring-ai-mcp/src/main/java/com/baeldung/springai/mcp/test/ExchangeRateService.java

@@ -0,0 +1,26 @@
+package com.baeldung.springai.mcp.test;
+
+import org.springframework.stereotype.Service;
+import org.springframework.web.client.RestClient;
+
+@Service
+public class ExchangeRateService {
+
+    private static final String FRANKFURTER_URL = "https://api.frankfurter.dev/v1/latest?base={base}";
+
+    private final RestClient restClient;
+
+    public ExchangeRateService(RestClient.Builder restClientBuilder) {
+        this.restClient = restClientBuilder.build();
+    }
+
+    public ExchangeRateResponse getLatestExchangeRate(String base) {
+        if (base == null || base.isBlank()) {
+            throw new IllegalArgumentException("base is required");
+        }
+        return restClient.get()
+            .uri(FRANKFURTER_URL, base.trim().toUpperCase())
+            .retrieve()
+            .body(ExchangeRateResponse.class);
+    }
+}

spring-ai-modules/spring-ai-mcp/src/main/java/com/baeldung/springai/mcp/test/TestMcpApplication.java

@@ -0,0 +1,23 @@
+package com.baeldung.springai.mcp.test;
+
+import org.springframework.ai.model.anthropic.autoconfigure.AnthropicChatAutoConfiguration;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.annotation.PropertySource;
+
+/**
+ * Excluding the below auto-configuration to avoid start up
+ * failure. Its corresponding starter is present on the classpath but is
+ * only needed by the MCP client application.
+ */
+@SpringBootApplication(exclude = {
+    AnthropicChatAutoConfiguration.class
+})
+@PropertySource("classpath:application-test-mcp-server.properties")
+public class TestMcpApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(TestMcpApplication.class, args);
+    }
+
+}

spring-ai-modules/spring-ai-mcp/src/main/resources/application-test-mcp-server.properties

@@ -0,0 +1 @@
+com.baeldung.author-tools.enabled=false

spring-ai-modules/spring-ai-mcp/src/test/java/com/baeldung/springai/mcp/test/ExchangeRateMcpToolSseIntegrationTest.java

@@ -0,0 +1,77 @@
+package com.baeldung.springai.mcp.test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.Mockito.when;
+
+import java.util.Map;
+import java.util.Objects;
+
+import io.modelcontextprotocol.client.McpSyncClient;
+import io.modelcontextprotocol.spec.McpSchema;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.mock.mockito.MockBean;
+import org.springframework.boot.test.web.server.LocalServerPort;
+
+@SpringBootTest(
+    webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT
+)
+class ExchangeRateMcpToolSseIntegrationTest {
+
+    @LocalServerPort
+    private int port;
+
+    @Autowired
+    private TestMcpClientFactory testMcpClientFactory;
+
+    @MockBean
+    private ExchangeRateService exchangeRateService;
+
+    private McpSyncClient client;
+
+    @BeforeEach
+    void setUp() {
+        client = testMcpClientFactory.create("http://localhost:" + port);
+        client.initialize();
+    }
+
+    @AfterEach
+    void cleanUp() {
+        client.closeGracefully();
+    }
+
+    @Test
+    void whenMcpClientListTools_thenTheToolIsRegistered() {
+        boolean registered = client.listTools().tools().stream()
+            .anyMatch(tool -> Objects.equals(tool.name(), "getLatestExchangeRate"));
+        assertThat(registered).isTrue();
+    }
+
+    @Test
+    void whenMcpClientCallTool_thenTheToolReturnsMockedResponse() {
+        when(exchangeRateService.getLatestExchangeRate("GBP")).thenReturn(
+            new ExchangeRateResponse(1.0, "GBP", "2026-03-08", Map.of("USD", 1.27))
+        );
+
+        McpSchema.Tool exchangeRateTool = client.listTools().tools().stream()
+            .filter(tool -> "getLatestExchangeRate".equals(tool.name()))
+            .findFirst()
+            .orElseThrow();
+
+        String argumentName = exchangeRateTool.inputSchema().properties().keySet().stream()
+            .findFirst()
+            .orElseThrow();
+
+        McpSchema.CallToolResult result = client.callTool(
+            new McpSchema.CallToolRequest("getLatestExchangeRate", Map.of(argumentName, "GBP"))
+        );
+
+        assertThat(result).isNotNull();
+        assertThat(result.isError()).isFalse();
+        assertTrue(result.toString().contains("GBP"));
+    }
+}

spring-ai-modules/spring-ai-mcp/src/test/java/com/baeldung/springai/mcp/test/ExchangeRateMcpToolStreamableIntegrationTest.java

@@ -0,0 +1,79 @@
+package com.baeldung.springai.mcp.test;
+
+import io.modelcontextprotocol.client.McpSyncClient;
+import io.modelcontextprotocol.spec.McpSchema;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.mock.mockito.MockBean;
+import org.springframework.boot.test.web.server.LocalServerPort;
+
+import java.util.Map;
+import java.util.Objects;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.Mockito.when;
+
+@SpringBootTest(
+    webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT,
+    properties = "spring.ai.mcp.server.protocol=streamable"
+)
+class ExchangeRateMcpToolStreamableIntegrationTest {
+
+    @LocalServerPort
+    private int port;
+
+    @MockBean
+    private ExchangeRateService exchangeRateService;
+
+    @Autowired
+    private TestMcpClientFactory testMcpClientFactory;
+
+    private McpSyncClient client;
+
+    @BeforeEach
+    void setUp() {
+        client = testMcpClientFactory.create("http://localhost:" + port);
+        client.initialize();
+    }
+
+    @AfterEach
+    void cleanUp() {
+        client.close();
+    }
+
+    @Test
+    void whenMcpClientListTools_thenTheToolIsRegistered() {
+        boolean registered = client.listTools().tools().stream()
+            .anyMatch(tool -> Objects.equals(tool.name(), "getLatestExchangeRate"));
+        assertThat(registered).isTrue();
+    }
+
+    @Test
+    void whenMcpClientCallTool_thenTheToolReturnsMockedResponse() {
+        when(exchangeRateService.getLatestExchangeRate("GBP")).thenReturn(
+            new ExchangeRateResponse(1.0, "GBP", "2026-03-08", Map.of("USD", 1.27))
+        );
+
+        McpSchema.Tool exchangeRateTool = client.listTools().tools().stream()
+            .filter(tool -> "getLatestExchangeRate".equals(tool.name()))
+            .findFirst()
+            .orElseThrow();
+
+        String argumentName = exchangeRateTool.inputSchema().properties().keySet().stream()
+            .findFirst()
+            .orElseThrow();
+
+        McpSchema.CallToolResult result = client.callTool(
+            new McpSchema.CallToolRequest("getLatestExchangeRate", Map.of(argumentName, "GBP"))
+        );
+
+        assertThat(result).isNotNull();
+        assertThat(result.isError()).isFalse();
+        assertTrue(result.toString().contains("GBP"));
+    }
+}

spring-ai-modules/spring-ai-mcp/src/test/java/com/baeldung/springai/mcp/test/ExchangeRateMcpToolUnitTest.java

@@ -0,0 +1,31 @@
+package com.baeldung.springai.mcp.test;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+class ExchangeRateMcpToolUnitTest {
+
+    @Test
+    void whenBaseIsNotBlank_thenGetExchangeRateShouldReturnResponse() {
+        ExchangeRateService exchangeRateService = mock(ExchangeRateService.class);
+        ExchangeRateResponse expected = new ExchangeRateResponse(
+            1.0,
+            "GBP",
+            "2026-03-08",
+            Map.of("USD", 1.27, "EUR", 1.17)
+        );
+        when(exchangeRateService.getLatestExchangeRate("gbp")).thenReturn(expected);
+
+        ExchangeRateMcpTool tool = new ExchangeRateMcpTool(exchangeRateService);
+        ExchangeRateResponse actual = tool.getLatestExchangeRate("gbp");
+
+        assertThat(actual).isEqualTo(expected);
+        verify(exchangeRateService).getLatestExchangeRate("gbp");
+    }
+}

spring-ai-modules/spring-ai-mcp/src/test/java/com/baeldung/springai/mcp/test/TestMcpClientFactory.java

@@ -0,0 +1,33 @@
+package com.baeldung.springai.mcp.test;
+
+import io.modelcontextprotocol.client.McpClient;
+import io.modelcontextprotocol.client.McpSyncClient;
+import io.modelcontextprotocol.client.transport.HttpClientSseClientTransport;
+import io.modelcontextprotocol.client.transport.HttpClientStreamableHttpTransport;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.stereotype.Component;
+
+@Component
+public class TestMcpClientFactory {
+
+    private final String protocol;
+
+    public TestMcpClientFactory(@Value("${spring.ai.mcp.server.protocol:sse}") String protocol) {
+        this.protocol = protocol;
+    }
+
+    public McpSyncClient create(String baseUrl) {
+        String resolvedProtocol = protocol.trim().toLowerCase();
+        return switch (resolvedProtocol) {
+            case "sse" -> McpClient.sync(HttpClientSseClientTransport.builder(baseUrl)
+                .sseEndpoint("/sse")
+                .build()
+            ).build();
+            case "streamable" -> McpClient.sync(HttpClientStreamableHttpTransport.builder(baseUrl)
+                .endpoint("/mcp")
+                .build()
+            ).build();
+            default -> throw new IllegalArgumentException("Unknown MCP protocol: " + protocol);
+        };
+    }
+}