JUnit5 断言帮助用测试用例的实际输出来验证期望的输出。为简单起见，所有 JUnit Jupiter 断言是org.junit.jupiter.Assertions类中的静态方法。
Table of Contents
Assertions.assertEquals() and Assertions.assertNotEquals()
Assertions.assertArrayEquals()
Assertions.assertIterableEquals()
Assertions.assertLinesMatch()
Assertions.assertNotNull() and Assertions.assertNull()
Assertions.assertNotSame() and Assertions.assertSame()
Assertions.assertTimeout() and Assertions.assertTimeoutPreemptively()
Assertions.assertTrue() and Assertions.assertFalse()
Assertions.assertThrows()
Assertions.fail()
Assertions.assertEquals()和Assertions.assertNotEquals()示例
使用Assertions.assertEquals()断言期望值等于实际值。 assertEquals()针对不同的数据类型（例如， int，short，float，char等。它还支持传递的错误消息，以防万一测试失败。 例如：
public static void assertEquals(int expected, int actual) public static void assertEquals(int expected, int actual, String message) public static void assertEquals(int expected, int actual, Supplier<String> messageSupplier)
void testCase() { //Test will pass Assertions.assertEquals(4, Calculator.add(2, 2)); //Test will fail Assertions.assertEquals(3, Calculator.add(2, 2), "Calculator.add(2, 2) test failed"); //Test will fail Supplier<String> messageSupplier = ()-> "Calculator.add(2, 2) test failed"; Assertions.assertEquals(3, Calculator.add(2, 2), messageSupplier); }
类似地，Assertions.assertNotEquals()方法用于断言期望值不等于实际值。 与assertEquals()相比，assertNotEquals()不会针对不同的数据类型重载方法，而仅接受Object。
public static void assertNotEquals(Object expected, Object actual) public static void assertNotEquals(Object expected, Object actual, String message) public static void assertNotEquals(Object expected, Object actual, Supplier<String> messageSupplier)
void testCase() { //Test will pass Assertions.assertNotEquals(3, Calculator.add(2, 2)); //Test will fail Assertions.assertNotEquals(4, Calculator.add(2, 2), "Calculator.add(2, 2) test failed"); //Test will fail Supplier<String> messageSupplier = ()-> "Calculator.add(2, 2) test failed"; Assertions.assertNotEquals(4, Calculator.add(2, 2), messageSupplier); }
Assertions.assertArrayEquals()示例
与assertEquals()相似，assertArrayEquals()对数组执行相同的操作，即断言期望数组等于实际数组。它还具有针对不同数据类型的重载方法，例如boolean[]，char[]，int[]等。它还支持在测试失败的情况下传递要打印的错误消息。 例如：
public static void assertArrayEquals(int[] expected, int[] actual) public static void assertArrayEquals(int[] expected, int[] actual, String message) public static void assertArrayEquals(int[] expected, int[] actual, Supplier<String> messageSupplier)
void testCase() { //Test will pass Assertions.assertArrayEquals(new int[]{1,2,3}, new int[]{1,2,3}, "Array Equal Test"); //Test will fail because element order is different Assertions.assertArrayEquals(new int[]{1,2,3}, new int[]{1,3,2}, "Array Equal Test"); //Test will fail because number of elements are different Assertions.assertArrayEquals(new int[]{1,2,3}, new int[]{1,2,3,4}, "Array Equal Test"); }
Assertions.assertIterableEquals()示例
它断言期望和实际的可迭代项高度相等。 高度相等意味着集合中元素的数量和顺序必须相同； 以及迭代元素必须相等。
它还有 3 种重载方法。
public static void assertIterableEquals(Iterable<?> expected, Iterable> actual) public static void assertIterableEquals(Iterable<?> expected, Iterable> actual, String message) public static void assertIterableEquals(Iterable<?> expected, Iterable> actual, Supplier<String> messageSupplier)
@Test void testCase() { Iterable<Integer> listOne = new ArrayList<>(Arrays.asList(1,2,3,4)); Iterable<Integer> listTwo = new ArrayList<>(Arrays.asList(1,2,3,4)); Iterable<Integer> listThree = new ArrayList<>(Arrays.asList(1,2,3)); Iterable<Integer> listFour = new ArrayList<>(Arrays.asList(1,2,4,3)); //Test will pass Assertions.assertIterableEquals(listOne, listTwo); //Test will fail Assertions.assertIterableEquals(listOne, listThree); //Test will fail Assertions.assertIterableEquals(listOne, listFour); }
Assertions.assertLinesMatch()示例
它断言期望的字符串列表与实际列表相匹配。 将一个字符串与另一个字符串匹配的逻辑是：
- 检查expected.equals(actual) –如果是，则继续下一对
- 否则将expected视为正则表达式，并通过String.matches(String) 检查–如果是，则继续下一对
- 否则检查expected行是否为快进标记，如果是，则相应地应用快速前行并转到 1。
有效的快进标记是以>>开头和结尾并且至少包含 4 个字符的字符串。 快进文字之间的任何字符都将被丢弃。
>>>> >> stacktrace >> >> single line, non Integer.parse()-able comment >>
Assertions.assertNotNull()和Assertions.assertNull()示例
assertNotNull()断言实际值不为空。 类似地，assertNull()方法断言实际值为空。 两者都有三种重载方法。
public static void assertNotNull(Object actual)
public static void assertNotNull(Object actual, String message)
public static void assertNotNull(Object actual, Supplier<String> messageSupplier)
public static void assertEquals(Object actual)
public static void assertEquals(Object actual, String message)
public static void assertEquals(Object actual, Supplier<String> messageSupplier)
@Test void testCase() { String nullString = null; String notNullString = "howtodoinjava.com"; //Test will pass Assertions.assertNotNull(notNullString); //Test will fail Assertions.assertNotNull(nullString); //Test will pass Assertions.assertNull(nullString); // Test will fail Assertions.assertNull(notNullString); }
Assertions.assertNotSame()和Assertions.assertSame()示例
assertNotSame()断言预期和实际不引用同一对象。 同样，assertSame()方法断言，预期和实际引用完全相同的对象。 两者都有三种重载方法。
public static void assertNotSame(Object actual) public static void assertNotSame(Object actual, String message) public static void assertNotSame(Object actual, Supplier<> messageSupplier) public static void assertSame(Object actual) public static void assertSame(Object actual, String message) public static void assertSame(Object actual, Supplier<String> messageSupplier)
@Test void testCase() { String originalObject = "howtodoinjava.com"; String cloneObject = originalObject; String otherObject = "example.com"; //Test will pass Assertions.assertNotSame(originalObject, otherObject); //Test will fail Assertions.assertNotSame(originalObject, cloneObject); //Test will pass Assertions.assertSame(originalObject, cloneObject); // Test will fail Assertions.assertSame(originalObject, otherObject); }
Assertions.assertTimeout()和Assertions.assertTimeoutPreemptively()示例
assertTimeout()和assertTimeoutPreemptively()均用于测试长时间运行的任务。 如果测试用例中的给定任务花费的时间超过指定的持续时间，则测试将失败。
两种方法之间唯一的区别是assertTimeoutPreemptively()中的设置，如果超过超时，Executable或ThrowingSupplier的执行将被抢先中止。 在assertTimeout()的情况下，不会中断Executable或ThrowingSupplier。
public static void assertTimeout(Duration timeout, Executable executable) public static void assertTimeout(Duration timeout, Executable executable, String message) public static void assertTimeout(Duration timeout, Executable executable, Supplier<String> messageSupplier) public static void assertTimeout(Duration timeout, ThrowingSupplier<T> supplier, String message) public static void assertTimeout(Duration timeout, ThrowingSupplier<T> supplier, Supplier<String> messageSupplier)
@Test void testCase() { //This will pass Assertions.assertTimeout(Duration.ofMinutes(1), () -> { return "result"; }); //This will fail Assertions.assertTimeout(Duration.ofMillis(100), () -> { Thread.sleep(200); return "result"; }); //This will fail Assertions.assertTimeoutPreemptively(Duration.ofMillis(100), () -> { Thread.sleep(200); return "result"; }); }
Assertions.assertTrue()和Assertions.assertFalse()示例
assertTrue()断言BooleanSupplier提供的条件为真。 类似地，assertFalse()断言提供的条件为假。 它具有以下重载方法：
public static void assertTrue(boolean condition) public static void assertTrue(boolean condition, String message) public static void assertTrue(boolean condition, Supplier<String> messageSupplier) public static void assertTrue(BooleanSupplier booleanSupplier) public static void assertTrue(BooleanSupplier booleanSupplier, String message) public static void assertTrue(BooleanSupplier booleanSupplier, Supplier<String> messageSupplier) public static void assertFalse(boolean condition) public static void assertFalse(boolean condition, String message) public static void assertFalse(boolean condition, Supplier<String> messageSupplier) public static void assertFalse(BooleanSupplier booleanSupplier) public static void assertFalse(BooleanSupplier booleanSupplier, String message) public static void assertFalse(BooleanSupplier booleanSupplier, Supplier<String> messageSupplier)
@Test void testCase() { boolean trueBool = true; boolean falseBool = false; Assertions.assertTrue(trueBool); Assertions.assertTrue(falseBool, "test execution message"); Assertions.assertTrue(falseBool, AppTest::message); Assertions.assertTrue(AppTest::getResult, AppTest::message); Assertions.assertFalse(falseBool); Assertions.assertFalse(trueBool, "test execution message"); Assertions.assertFalse(trueBool, AppTest::message); Assertions.assertFalse(AppTest::getResult, AppTest::message); } private static String message () { return "Test execution result"; } private static boolean getResult () { return true; }
Assertions.assertThrows()示例
它断言所提供的Executable的执行将引发expectedType的异常并返回该异常。
public static <T extends Throwable> T assertThrows(Class<T> expectedType, Executable executable)
@Test void testCase() { Throwable exception = Assertions.assertThrows(IllegalArgumentException.class, () -> { throw new IllegalArgumentException("error message"); }); }
Assertions.fail()示例
fail()方法仅使测试失败。 它具有以下重载方法：
public static void fail(String message) public static void fail(Throwable cause) public static void fail(String message, Throwable cause) public static void fail(Supplier<String> messageSupplier)