Add rest-client-test module: @RestClientTest on Boot 4.1, Jackson 3 by default, and the RestClient-vs-RestTemplate root-URI matching trap (post #49)

rest-client-test/src/test/java/com/ankurm/restclienttest/HttpInterfaceClientTest.java

@@ -0,0 +1,54 @@
+package com.ankurm.restclienttest;
+
+import tools.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.restclient.test.autoconfigure.RestClientTest;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.client.MockRestServiceServer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
+
+/**
+ * {@link EmployeeHttpInterface} has no class {@code @RestClientTest} can point at directly - it
+ * is a bare interface, and the real bean only exists because {@link AppConfig}'s
+ * {@code @Bean} method builds it from an {@code HttpServiceProxyFactory}. Passing the
+ * {@code @Configuration} class itself as the slice's "component" is what gets that bean (and
+ * the underlying {@code RestClient} it is built from) into the test context at all; the mocking
+ * code underneath is otherwise identical to {@link RestClientEmployeeTest}.
+ */
+@RestClientTest(components = AppConfig.class)
+class HttpInterfaceClientTest {
+
+    @Autowired
+    private MockRestServiceServer mockServer;
+
+    @Autowired
+    private EmployeeHttpInterface employeeHttpInterface;
+
+    @Autowired
+    private ObjectMapper objectMapper;
+
+    @Test
+    void whenGetEmployeeById_thenHttpInterfaceReturnsEmployee() throws Exception {
+        Employee mockEmployee = new Employee(3, "Daniel", "O", "[email protected]");
+        String employeeJson = objectMapper.writeValueAsString(mockEmployee);
+
+        mockServer.expect(requestTo("http://hr-api.example.com/employees/3"))
+                .andRespond(withSuccess(employeeJson, MediaType.APPLICATION_JSON));
+
+        Employee result = employeeHttpInterface.getEmployeeById(3);
+
+        assertThat(result).isNotNull();
+        assertThat(result.id()).isEqualTo(3);
+        assertThat(result.firstName()).isEqualTo("Daniel");
+
+        mockServer.verify();
+
+        Capture.write("04-http-interface-client.txt",
+                "A declarative @HttpExchange interface client, mocked the same way as a hand-written one",
+                "requestTo(\"http://hr-api.example.com/employees/3\") -> 200 OK " + employeeJson + "\nresult = " + result);
+    }
+}