【Junit】OkHttpClientのテストを実装する in gradle

dependencies {
    // OkHttpClient
    implementation 'com.squareup.okhttp3:okhttp:4.9.3'
    // Gson for JSON deserialization
    implementation 'com.google.code.gson:gson:2.8.9'

    // JUnit5
    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.7.0'
    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.7.0'

    // Mockito
    testImplementation 'org.mockito:mockito-core:3.9.0'
    testImplementation 'org.mockito:mockito-inline:3.9.0'

    // AssertJ for better assertions
    testImplementation 'org.assertj:assertj-core:3.19.0'
}

import okhttp3.*;
import java.io.IOException;
import com.google.gson.Gson;

public class ApiClient {

    private final OkHttpClient client;
    private final String baseUrl;
    private final Gson gson;

    public ApiClient(String baseUrl) {
        this.client = new OkHttpClient();
        this.baseUrl = baseUrl;
        this.gson = new Gson();
    }

    public <T> T sendPostRequest(String endpoint, String jsonBody, String authToken, Class<T> responseType) throws IOException {
        RequestBody body = RequestBody.create(jsonBody, MediaType.get("application/json; charset=utf-8"));

        Request request = new Request.Builder()
                .url(baseUrl + endpoint)
                .addHeader("Authorization", "Bearer " + authToken)
                .addHeader("Content-Type", "application/json")
                .post(body)
                .build();

        try (Response response = client.newCall(request).execute()) {
            if (!response.isSuccessful()) {
                throw new IOException("Unexpected code " + response);
            }

            // レスポンスをオブジェクトに変換して返す
            return gson.fromJson(response.body().string(), responseType);
        }
    }
}

import okhttp3.*;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.mockito.ArgumentCaptor;

import static org.mockito.Mockito.*;
import static org.assertj.core.api.Assertions.*;

import java.io.IOException;

class ApiClientTest {

    private OkHttpClient mockHttpClient;
    private ApiClient apiClient;
    private Call mockCall;
    private Response mockResponse;

    @BeforeEach
    void setUp() {
        mockHttpClient = mock(OkHttpClient.class);
        mockCall = mock(Call.class);
        apiClient = new ApiClient("https://api.example.com");
    }

    @Test
    void testSendPostRequest() throws IOException {
        // モックされたレスポンスの設定
        ResponseBody mockResponseBody = ResponseBody.create("{\"success\": true}", MediaType.get("application/json"));
        mockResponse = new Response.Builder()
                .request(new Request.Builder().url("https://api.example.com/post-endpoint").build())
                .protocol(Protocol.HTTP_1_1)
                .code(200)
                .message("OK")
                .body(mockResponseBody)
                .build();

        // モックが呼び出されたときにレスポンスを返すように設定
        when(mockCall.execute()).thenReturn(mockResponse);
        when(mockHttpClient.newCall(any(Request.class))).thenReturn(mockCall);

        // リクエストの検証用にArgumentCaptorを使う
        ArgumentCaptor<Request> requestCaptor = ArgumentCaptor.forClass(Request.class);

        // 実際のテスト対象メソッドを呼び出し
        TestResponse response = apiClient.sendPostRequest("/post-endpoint", "{\"key\":\"value\"}", "your-token", TestResponse.class);

        // レスポンスが正しくオブジェクトに変換されているかを検証
        assertThat(response.isSuccess()).isTrue();

        // リクエストの内容をキャプチャして検証
        verify(mockHttpClient).newCall(requestCaptor.capture());
        Request capturedRequest = requestCaptor.getValue();

        // リクエスト URL、ヘッダー、ボディの検証
        assertThat(capturedRequest.url().toString()).isEqualTo("https://api.example.com/post-endpoint");
        assertThat(capturedRequest.header("Authorization")).isEqualTo("Bearer your-token");
        assertThat(capturedRequest.header("Content-Type")).isEqualTo("application/json");
        assertThat(capturedRequest.body()).isNotNull();
    }

    // テスト用のレスポンスクラス
    static class TestResponse {
        private boolean success;

        public boolean isSuccess() {
            return success;
        }

        public void setSuccess(boolean success) {
            this.success = success;
        }
    }
}