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/RestTemplateEmployeeTest.java

@@ -0,0 +1,52 @@
+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;
+
+/**
+ * Same job, built on {@code RestTemplate} instead of {@code RestClient}.
+ * {@code @RestClientTest} auto-configures a {@code RestTemplateBuilder} too, so any
+ * {@code RestTemplate} built from it is wired through the same {@code MockRestServiceServer} -
+ * the mocking code below is identical to {@link RestClientEmployeeTest}'s, line for line.
+ */
+@RestClientTest(EmployeeTemplateClient.class)
+class RestTemplateEmployeeTest {
+
+    @Autowired
+    private MockRestServiceServer mockServer;
+
+    @Autowired
+    private EmployeeTemplateClient employeeTemplateClient;
+
+    @Autowired
+    private ObjectMapper objectMapper;
+
+    @Test
+    void whenGetEmployeeById_thenReturnsEmployee() throws Exception {
+        Employee mockEmployee = new Employee(2, "Priya", "V", "[email protected]");
+        String employeeJson = objectMapper.writeValueAsString(mockEmployee);
+
+        mockServer.expect(requestTo("/employees/2"))
+                .andRespond(withSuccess(employeeJson, MediaType.APPLICATION_JSON));
+
+        Employee result = employeeTemplateClient.getEmployeeById(2);
+
+        assertThat(result).isNotNull();
+        assertThat(result.id()).isEqualTo(2);
+        assertThat(result.firstName()).isEqualTo("Priya");
+
+        mockServer.verify();
+
+        Capture.write("02-resttemplate-same-mocking-code.txt",
+                "RestTemplate-based EmployeeTemplateClient, identical MockRestServiceServer code",
+                "requestTo(\"/employees/2\") -> 200 OK " + employeeJson + "\nresult = " + result);
+    }
+}