System.out.println()的JUnit测试

我需要为一个设计很差的旧应用程序编写JUnit测试，该应用程序正在向标准输出写入大量错误消息。当getResponse(String request)方法行为正确时，它返回一个XML响应:

@BeforeClass
public static void setUpClass() throws Exception {
    Properties queries = loadPropertiesFile("requests.properties");
    Properties responses = loadPropertiesFile("responses.properties");
    instance = new ResponseGenerator(queries, responses);
}

@Test
public void testGetResponse() {
    String request = "<some>request</some>";
    String expResult = "<some>response</some>";
    String result = instance.getResponse(request);
    assertEquals(expResult, result);
}

但是当它得到格式不正确的XML或不理解请求时，它返回null并将一些东西写入标准输出。

在JUnit中是否有方法断言控制台输出?捕捉以下情况:

System.out.println("match found: " + strExpr);
System.out.println("xml not well formed: " + e.getMessage());

当前回答

虽然这个问题已经很老了，而且已经有了很好的答案，但我想提供一个替代方案。我喜欢dfa的答案，但是我想在不同的项目中有一些可重用的东西，而不复制配置，所以我用它创建了一个库，并想贡献给社区。它被称为控制台捕捉器，你可以添加下面的代码片段:

<dependency>
    <groupId>io.github.hakky54</groupId>
    <artifactId>consolecaptor</artifactId>
    <version>1.0.0</version>
    <scope>test</scope>
</dependency>

示例类

public class FooService {

    public void sayHello() {
        System.out.println("Keyboard not responding. Press any key to continue...");
        System.err.println("Congratulations, you are pregnant!");
    }

}

单元测试

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

import nl.altindag.console.ConsoleCaptor;
import org.junit.jupiter.api.Test;

public class FooServiceTest {

    @Test
    public void captureStandardAndErrorOutput() {
        ConsoleCaptor consoleCaptor = new ConsoleCaptor();

        FooService fooService = new FooService();
        fooService.sayHello();

        assertThat(consoleCaptor.getStandardOutput()).contains("Keyboard not responding. Press any key to continue...");
        assertThat(consoleCaptor.getErrorOutput()).contains("Congratulations, you are pregnant!");
        
        consoleCaptor.close();
    }
}

2021-07-14 20:36:05

其他回答

您可以设置“系统”。输出输出流通过setOut()(和for in和err)。你能把它重定向到一个打印流，记录到一个字符串，然后检查它吗?这似乎是最简单的机制。

(我主张，在某些阶段，将应用程序转换为一些日志框架-但我怀疑你已经意识到这一点!)

2009-07-13 13:19:46

完整的JUnit 5示例来测试系统。Out(更换when部分):

package learning;

import static org.assertj.core.api.BDDAssertions.then;

import java.io.ByteArrayOutputStream;
import java.io.PrintStream;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

class SystemOutLT {

    private PrintStream originalSystemOut;
    private ByteArrayOutputStream systemOutContent;

    @BeforeEach
    void redirectSystemOutStream() {

        originalSystemOut = System.out;

        // given
        systemOutContent = new ByteArrayOutputStream();
        System.setOut(new PrintStream(systemOutContent));
    }

    @AfterEach
    void restoreSystemOutStream() {
        System.setOut(originalSystemOut);
    }

    @Test
    void shouldPrintToSystemOut() {

        // when
        System.out.println("example");

        then(systemOutContent.toString()).containsIgnoringCase("example");
    }
}

2018-05-31 12:31:32

有点偏离主题，但如果有些人(比如我，当我第一次发现这个线程时)可能对通过SLF4J捕获日志输出感兴趣，common -testing的JUnit @Rule可能会有所帮助:

public class FooTest {
    @Rule
    public final ExpectedLogs logs = new ExpectedLogs() {{
        captureFor(Foo.class, LogLevel.WARN);
    }};

    @Test
    public void barShouldLogWarning() {
        assertThat(logs.isEmpty(), is(true)); // Nothing captured yet.

        // Logic using the class you are capturing logs for:
        Foo foo = new Foo();
        assertThat(foo.bar(), is(not(nullValue())));

        // Assert content of the captured logs:
        assertThat(logs.isEmpty(), is(false));
        assertThat(logs.contains("Your warning message here"), is(true));
    }
}

免责声明:

我开发了这个库，因为我找不到任何适合我自己需求的解决方案。目前只有log4j、log4j2和logback的绑定可用，但我很乐意添加更多绑定。

2014-12-11 08:29:34

<dependency>
    <groupId>io.github.hakky54</groupId>
    <artifactId>consolecaptor</artifactId>
    <version>1.0.0</version>
    <scope>test</scope>
</dependency>

示例类

public class FooService {

    public void sayHello() {
        System.out.println("Keyboard not responding. Press any key to continue...");
        System.err.println("Congratulations, you are pregnant!");
    }

}

单元测试

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

import nl.altindag.console.ConsoleCaptor;
import org.junit.jupiter.api.Test;

public class FooServiceTest {

    @Test
    public void captureStandardAndErrorOutput() {
        ConsoleCaptor consoleCaptor = new ConsoleCaptor();

        FooService fooService = new FooService();
        fooService.sayHello();

        assertThat(consoleCaptor.getStandardOutput()).contains("Keyboard not responding. Press any key to continue...");
        assertThat(consoleCaptor.getErrorOutput()).contains("Congratulations, you are pregnant!");
        
        consoleCaptor.close();
    }
}

2021-07-14 20:36:05

使用ByteArrayOutputStream和System。setXXX很简单:

private final ByteArrayOutputStream outContent = new ByteArrayOutputStream();
private final ByteArrayOutputStream errContent = new ByteArrayOutputStream();
private final PrintStream originalOut = System.out;
private final PrintStream originalErr = System.err;

@Before
public void setUpStreams() {
    System.setOut(new PrintStream(outContent));
    System.setErr(new PrintStream(errContent));
}

@After
public void restoreStreams() {
    System.setOut(originalOut);
    System.setErr(originalErr);
}

示例测试用例:

@Test
public void out() {
    System.out.print("hello");
    assertEquals("hello", outContent.toString());
}

@Test
public void err() {
    System.err.print("hello again");
    assertEquals("hello again", errContent.toString());
}

我使用这段代码来测试命令行选项(断言-version输出版本字符串，等等)

编辑: 这个答案的先前版本在测试后称为System.setOut(null);这就是NullPointerExceptions注释引用的原因。

2009-07-13 13:51:11

System.out.println()的JUnit测试

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