08-单元测试

1. JUnit5 简述

Spring Boot 2.2.0 版本开始引入 JUnit 5 作为单元测试默认库。

作为最新版本的 JUnit 框架，JUnit5 与之前版本的 Junit 框架有很大的不同。由 3 个不同子项目的几个不同模块组成。

JUnit 5 = JUnit Platform + JUnit Jupiter + JUnit Vintage

• 【JUnit Platform】Junit Platform 是在 JVM 上启动测试框架的基础，不仅支持 JUnit 自制的测试引擎，其他测试引擎也都可以接入；
• 【JUnit Jupiter】JUnit Jupiter提供了 JUnit5 的新的编程模型，是 JUnit5 新特性的核心。内部包含了一个测试引擎，用于在 Junit Platform 上运行；
• 【JUnit Vintage】由于 JUint 已经发展多年，为了照顾老的项目，JUnit Vintage 提供了兼容 JUnit4.x、JUnit3.x 的测试引擎。

导入 test-starter，本人学习使用的 2.4.3 的 SpringBoot：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
</dependency>

查看 Maven-Dependencies：

https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-2.4-Release-Notes

【JUnit 5’s Vintage Engine Removed from spring-boot-starter-test】If you upgrade to Spring Boot 2.4 and see test compilation errors for JUnit classes such as org.junit.Test, this may be because JUnit 5’s vintage engine has been removed from spring-boot-starter-test. The vintage engine allows tests written with JUnit 4 to be run by JUnit 5. If you do not want to migrate your tests to JUnit 5 and wish to continue using JUnit 4, add a dependency on the Vintage Engine, as shown in the following example for Maven:

<dependency>
    <groupId>org.junit.vintage</groupId>
    <artifactId>junit-vintage-engine</artifactId>
    <scope>test</scope>
    <exclusions>
        <exclusion>
            <groupId>org.hamcrest</groupId>
            <artifactId>hamcrest-core</artifactId>
        </exclusion>
    </exclusions>
</dependency>

2. 常用注解

https://junit.org/junit5/docs/current/user-guide/#writing-tests-annotations

注解	介绍
@Test	表示方法是测试方法；但是与 JUnit4 的 @Test 不同，他的职责非常单一不能声明任何属性，拓展的测试将会由 Jupiter 提供额外测试
@Timeout	表示测试方法运行如果超过了指定时间将会返回错误
@Disabled	表示测试类或测试方法不执行，类似于 JUnit4 中的 @Ignore
@DisplayName	为测试类或者测试方法设置展示名称
@ExtendWith	为测试类或测试方法提供扩展类引用 @SpringBootTest=xxx+@ExtendWith(SpringExtension.class)
@BeforeEach	表示在每个单元测试之前执行
@AfterEach	表示在所有单元测试之前执行
@BeforeAll	表示在所有单元测试之前执行
@AfterAll	表示在所有单元测试之后执行
@Tag	表示单元测试类别，类似于 JUnit4 中的 @Categories
@RepeatedTest	表示方法可重复执行
@ParameterizedTest	表示方法是参数化测试，下方会有详细介绍

3. 断言

https://junit.org/junit5/docs/current/user-guide/#writing-tests-assertions

断言（assertions）是测试方法中的核心部分，用来对测试需要满足的条件进行验证。这些断言方法都是 org.junit.jupiter.api.Assertions 的静态方法。

• 简单断言
  
• 数组断言：通过 assertArrayEquals 方法来判断两个对象或原始类型的数组是否相等；
• 组合断言：assertAll 方法接受多个 org.junit.jupiter.api.Executable 函数式接口的实例作为要验证的断言，可以通过 lambda 表达式很容易的提供这些断言；
• 异常断言：Assertions.assertThrows() 测试方法的异常情况，配合函数式编程就可以进行使用；
• 超时断言：Assertions.assertTimeout() 为测试方法设置了超时时间；
• 快速失败：通过 fail 方法直接使得测试失败。

class AssertionsDemo {

    private final Calculator calculator = new Calculator();

    private final Person person = new Person("Jane", "Doe");

    @Test
    void standardAssertions() {
        assertEquals(2, calculator.add(1, 1));
        assertEquals(4, calculator.multiply(2, 2),
                "The optional failure message is now the last parameter");
        assertTrue('a' < 'b', () -> "Assertion messages can be lazily evaluated -- "
                + "to avoid constructing complex messages unnecessarily.");
    }

    @Test
    void groupedAssertions() {
        // In a grouped assertion all assertions are executed, and all
        // failures will be reported together.
        assertAll("person",
            () -> assertEquals("Jane", person.getFirstName()),
            () -> assertEquals("Doe", person.getLastName())
        );
    }

    @Test
    void dependentAssertions() {
        // Within a code block, if an assertion fails the
        // subsequent code in the same block will be skipped.
        assertAll("properties",
            () -> {
                String firstName = person.getFirstName();
                assertNotNull(firstName);

                // Executed only if the previous assertion is valid.
                assertAll("first name",
                    () -> assertTrue(firstName.startsWith("J")),
                    () -> assertTrue(firstName.endsWith("e"))
                );
            },
            () -> {
                // Grouped assertion, so processed independently
                // of results of first name assertions.
                String lastName = person.getLastName();
                assertNotNull(lastName);

                // Executed only if the previous assertion is valid.
                assertAll("last name",
                    () -> assertTrue(lastName.startsWith("D")),
                    () -> assertTrue(lastName.endsWith("e"))
                );
            }
        );
    }

    @Test
    void exceptionTesting() {
        Exception exception = assertThrows(ArithmeticException.class, () ->
            calculator.divide(1, 0));
        assertEquals("/ by zero", exception.getMessage());
    }

    @Test
    void timeoutNotExceeded() {
        // The following assertion succeeds.
        assertTimeout(ofMinutes(2), () -> {
            // Perform task that takes less than 2 minutes.
        });
    }

    @Test
    void timeoutNotExceededWithResult() {
        // The following assertion succeeds, and returns the supplied object.
        String actualResult = assertTimeout(ofMinutes(2), () -> {
            return "a result";
        });
        assertEquals("a result", actualResult);
    }

    @Test
    void timeoutNotExceededWithMethod() {
        // The following assertion invokes a method reference and returns an object.
        String actualGreeting = assertTimeout(ofMinutes(2), AssertionsDemo::greeting);
        assertEquals("Hello, World!", actualGreeting);
    }

    @Test
    void timeoutExceeded() {
        // The following assertion fails with an error message similar to:
        // execution exceeded timeout of 10 ms by 91 ms
        assertTimeout(ofMillis(10), () -> {
            // Simulate task that takes more than 10 ms.
            Thread.sleep(100);
        });
    }

    @Test
    void timeoutExceededWithPreemptiveTermination() {
        // The following assertion fails with an error message similar to:
        // execution timed out after 10 ms
        assertTimeoutPreemptively(ofMillis(10), () -> {
            // Simulate task that takes more than 10 ms.
            new CountDownLatch(1).await();
        });
    }

    private static String greeting() {
        return "Hello, World!";
    }

}

4. 前置条件

https://junit.org/junit5/docs/current/user-guide/#writing-tests-assumptions

JUnit 5 中的前置条件 「assumptions(假设)」类似于断言，不同之处在于不满足的断言会使得测试方法失败，而不满足的前置条件只会使得测试方法的执行终止。前置条件可以看成是测试方法执行的前提，当该前提不满足时，就没有继续执行的必要。

class AssumptionsDemo {

    private final Calculator calculator = new Calculator();

    @Test
    void testOnlyOnCiServer() {
        assumeTrue("CI".equals(System.getenv("ENV")));
        // remainder of test
    }

    @Test
    void testOnlyOnDeveloperWorkstation() {
        assumeTrue("DEV".equals(System.getenv("ENV")),
            () -> "Aborting test: not on developer workstation");
        // remainder of test
    }

    @Test
    void testInAllEnvironments() {
        assumingThat("CI".equals(System.getenv("ENV")),
            () -> {
                // perform these assertions only on the CI server
                assertEquals(2, calculator.divide(4, 2));
            });

        // perform these assertions in all environments
        assertEquals(42, calculator.multiply(6, 7));
    }

}

5. 嵌套测试

https://junit.org/junit5/docs/current/user-guide/#writing-tests-nested

补充：内层可以驱动外层的 @Before/After|Each/All，但外层不能驱动内层的。

@DisplayName("A stack")
class TestingAStackDemo {

    Stack<Object> stack;

    @Test
    @DisplayName("is instantiated with new Stack()")
    void isInstantiatedWithNew() {
        new Stack<>();
    }

    @Nested
    @DisplayName("when new")
    class WhenNew {

        @BeforeEach
        void createNewStack() {
            stack = new Stack<>();
        }

        @Test
        @DisplayName("is empty")
        void isEmpty() {
            assertTrue(stack.isEmpty());
        }

        @Test
        @DisplayName("throws EmptyStackException when popped")
        void throwsExceptionWhenPopped() {
            assertThrows(EmptyStackException.class, stack::pop);
        }

        @Test
        @DisplayName("throws EmptyStackException when peeked")
        void throwsExceptionWhenPeeked() {
            assertThrows(EmptyStackException.class, stack::peek);
        }

        @Nested
        @DisplayName("after pushing an element")
        class AfterPushing {

            String anElement = "an element";

            @BeforeEach
            void pushAnElement() {
                stack.push(anElement);
            }

            @Test
            @DisplayName("it is no longer empty")
            void isNotEmpty() {
                assertFalse(stack.isEmpty());
            }

            @Test
            @DisplayName("returns the element when popped and is empty")
            void returnElementWhenPopped() {
                assertEquals(anElement, stack.pop());
                assertTrue(stack.isEmpty());
            }

            @Test
            @DisplayName("returns the element when peeked but remains not empty")
            void returnElementWhenPeeked() {
                assertEquals(anElement, stack.peek());
                assertFalse(stack.isEmpty());
            }
        }
    }
}

6. 参数化测试

https://junit.org/junit5/docs/current/user-guide/#writing-tests-parameterized-tests

参数化注解	简述
@ValueSource	为参数化测试指定入参来源，支持 8 大基础类以及 String、Class 类型
@NullSource	表示为参数化测试提供一个 null 的入参
@EnumSource	表示为参数化测试提供一个枚举入参
@CsvFileSource	表示读取指定 CSV 文件内容作为参数化测试入参
@MethodSource	表示读取指定方法的返回值作为参数化测试入参（注意方法返回需要是一个流）

The following example demonstrates a parameterized test that uses the @ValueSource annotation to specify a String[] as the source of arguments.

@ParameterizedTest
@ValueSource(strings = { "racecar", "radar", "able was I ere I saw elba" })
void palindromes(String candidate) {
    assertTrue(StringUtils.isPalindrome(candidate));
}

When executing the above parameterized test method, each invocation will be reported separately. For instance, the ConsoleLauncher will print output similar to the following.

palindromes(String) ✔
├─ [1] candidate=racecar ✔
├─ [2] candidate=radar ✔
└─ [3] candidate=able was I ere I saw elba ✔

If you only need a single parameter, you can return a Stream of instances of the parameter type as demonstrated in the following example.

@ParameterizedTest
@MethodSource("stringProvider")
void testWithExplicitLocalMethodSource(String argument) {
    assertNotNull(argument);
}

static Stream<String> stringProvider() {
    return Stream.of("apple", "banana");
}

7. 迁移指南

在进行迁移的时候需要注意如下的变化：

• 注解在 org.junit.jupiter.api 包中，断言在 org.junit.jupiter.api.Assertions 类中，前置条件在 org.junit.jupiter.api.Assumptions 类中；
• 把 @Before 和 @After 替换成 @BeforeEach 和 @AfterEach；
• 把 @BeforeClass 和 @AfterClass 替换成 @BeforeAll 和 @AfterAll；
• 把 @Ignore 替换成 @Disabled；
• 把 @Category 替换成 @Tag；
• 把 @RunWith、@Rule 和 @ClassRule 替换成 @ExtendWith。