断言参考

基础断言

import static org.junit.jupiter.api.Assertions.*;

@Test
void basicAssertions() {
    assertEquals(4, 2 + 2);
    assertEquals("hello", result.toLowerCase());
    assertEquals(3.14, Math.PI, 0.01);  // 浮点数 delta

    assertNull(user.getMiddleName());
    assertNotNull(response.getBody());

    assertTrue(list.isEmpty());
    assertFalse(user.isBanned());

    assertArrayEquals(new int[]{1, 2, 3}, actual);

    // 带失败消息
    assertEquals(200, response.getStatus(), "期望 OK 状态");
}

assertThrows 与 assertDoesNotThrow

@Test
void exceptionAssertions() {
    IllegalArgumentException ex = assertThrows(
        IllegalArgumentException.class,
        () -> service.create(null)
    );
    assertEquals("名称不能为空", ex.getMessage());

    // 断言不抛出异常
    assertDoesNotThrow(() -> service.healthCheck());

    // assertThrowsExactly — 不接受子类
    assertThrowsExactly(
        NullPointerException.class,
        () -> parseNull()
    );
}

assertAll — 分组断言

@Test void userFieldsAreCorrect() { User user = service.findById(1L); // 即使某条断言失败，所有断言都会执行 assertAll("用户属性", () -> assertEquals("张三", user.getName()), () -> assertEquals("[email protected]", user.getEmail()), () -> assertTrue(user.isActive()), () -> assertNotNull(user.getCreatedAt()) ); }

assertTimeout 与 assertTimeoutPreemptively

import java.time.Duration;

@Test
void operationCompletesInTime() {
    String result = assertTimeout(Duration.ofSeconds(2), () -> {
        return processBigFile();
    });
    assertNotNull(result);
}

@Test
void operationAbortedIfTooSlow() {
    // 超时后中断执行（在新线程中运行）
    assertTimeoutPreemptively(Duration.ofMillis(500), () -> {
        Thread.sleep(200);
        return fetchData();
    });
}

假设条件 — assumeTrue / assumingThat

import static org.junit.jupiter.api.Assumptions.*;

@Test
void onlyRunOnLinux() {
    assumeTrue("Linux".equals(System.getProperty("os.name")));
    // 仅在 Linux 上运行，否则跳过（不是失败）
}

@Test
void conditionalBehavior() {
    assumingThat(
        Boolean.getBoolean("ci.build"),
        () -> {
            assertEquals(0, getWarnings().size());
        }
    );
    // 以下代码始终执行
    assertNotNull(mainResult);
}

AssertJ 自定义断言

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

@Test
void assertJExamples() {
    assertThat("你好，世界")
        .startsWith("你好")
        .hasSize(5);

    assertThat(list)
        .hasSize(3)
        .contains("苹果", "香蕉")
        .doesNotContain("樱桃");

    assertThatThrownBy(() -> service.divide(1, 0))
        .isInstanceOf(ArithmeticException.class)
        .hasMessage("/ by zero");
}