是否有可能以某种方式拦截日志记录(SLF4J + logback)并通过JUnit测试用例获取InputStream
(或其他可读的内容)......?
您可以创建自定义appender
public class TestAppender extends AppenderBase<LoggingEvent> {
static List<LoggingEvent> events = new ArrayList<>();
@Override
protected void append(LoggingEvent e) {
events.add(e);
}
}
并配置logback-test.xml以使用它。现在我们可以从测试中检查记录事件:
@Test
public void test() {
...
Assert.assertEquals(1, TestAppender.events.size());
...
}
Slf4j API不提供这种方式,但Logback提供了一个简单的解决方案。
您可以使用ListAppender
:whitebox logback appender,其中日志条目添加到public List
字段中,我们可以用它来进行断言。
这是一个简单的例子。
Foo类:
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class Foo {
static final Logger LOGGER = LoggerFactory.getLogger(Foo .class);
public void doThat() {
logger.info("start");
//...
logger.info("finish");
}
}
FooTest类:
import org.slf4j.LoggerFactory;
import ch.qos.logback.classic.Level;
import ch.qos.logback.classic.Logger;
import ch.qos.logback.classic.spi.ILoggingEvent;
import ch.qos.logback.core.read.ListAppender;
public class FooTest {
@Test
void doThat() throws Exception {
// get Logback Logger
Logger fooLogger = (Logger) LoggerFactory.getLogger(Foo.class);
// create and start a ListAppender
ListAppender<ILoggingEvent> listAppender = new ListAppender<>();
listAppender.start();
// add the appender to the logger
fooLogger.addAppender(listAppender);
// call method under test
Foo foo = new Foo();
foo.doThat();
// JUnit assertions
List<ILoggingEvent> logsList = listAppender.list;
assertEquals("start", logsList.get(0)
.getMessage());
assertEquals(Level.INFO, logsList.get(0)
.getLevel());
assertEquals("finish", logsList.get(1)
.getMessage());
assertEquals(Level.INFO, logsList.get(1)
.getLevel());
}
}
您还可以使用Matcher /断言库作为AssertJ或Hamcrest。
使用AssertJ,它将是:
import org.assertj.core.api.Assertions;
Assertions.assertThat(listAppender.list)
.extracting(ILoggingEvent::getMessage, ILoggingEvent::getLevel)
.containsExactly(Tuple.tuple("start", Level.INFO), Tuple.tuple("finish", Level.INFO));
你可以使用http://projects.lidalia.org.uk/slf4j-test/的slf4j-test。它通过它自己的slf4j api实现来替换整个logback slf4j实现,并提供一个api来对记录事件进行断言。
例:
<build>
<plugins>
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<configuration>
<classpathDependencyExcludes>
<classpathDependencyExcludes>ch.qos.logback:logback-classic</classpathDependencyExcludes>
</classpathDependencyExcludes>
</configuration>
</plugin>
</plugins>
</build>
public class Slf4jUser {
private static final Logger logger = LoggerFactory.getLogger(Slf4jUser.class);
public void aMethodThatLogs() {
logger.info("Hello World!");
}
}
public class Slf4jUserTest {
Slf4jUser slf4jUser = new Slf4jUser();
TestLogger logger = TestLoggerFactory.getTestLogger(Slf4jUser.class);
@Test
public void aMethodThatLogsLogsAsExpected() {
slf4jUser.aMethodThatLogs();
assertThat(logger.getLoggingEvents(), is(asList(info("Hello World!"))));
}
@After
public void clearLoggers() {
TestLoggerFactory.clear();
}
}
虽然创建自定义logback appender是一个很好的解决方案,但它只是第一步,你最终将最终开发/重新发明slf4j-test,如果你再进一步:spf4j-slf4j-test或其他我还不知道的框架。
您最终需要担心在内存中保留了多少事件,在记录错误(未断言)时进行单元测试失败,在测试失败时使调试日志可用等等......
免责声明:我是spf4j-slf4j-test的作者,我写了这个后端,以便能够更好地测试spf4j,这是一个关于如何使用spf4j-slf4j-test的例子的好地方。我实现的主要优势之一是减少我的构建输出(受Travis限制),同时仍然具有发生故障时所需的所有细节。
测试日志行时遇到问题:LOGGER.error(message,exception)。
http://projects.lidalia.org.uk/slf4j-test/中描述的解决方案也试图在异常上断言,并且重新创建堆栈跟踪并不容易(在我看来毫无价值)。
我这样解决了:
import org.junit.Test;
import org.slf4j.Logger;
import uk.org.lidalia.slf4jext.LoggerFactory;
import uk.org.lidalia.slf4jtest.TestLogger;
import uk.org.lidalia.slf4jtest.TestLoggerFactory;
import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.groups.Tuple.tuple;
import static uk.org.lidalia.slf4jext.Level.ERROR;
import static uk.org.lidalia.slf4jext.Level.INFO;
public class Slf4jLoggerTest {
private static final Logger LOGGER = LoggerFactory.getLogger(Slf4jLoggerTest.class);
private void methodUnderTestInSomeClassInProductionCode() {
LOGGER.info("info message");
LOGGER.error("error message");
LOGGER.error("error message with exception", new RuntimeException("this part is not tested"));
}
private static final TestLogger TEST_LOGGER = TestLoggerFactory.getTestLogger(Slf4jLoggerTest.class);
@Test
public void testForMethod() throws Exception {
// when
methodUnderTestInSomeClassInProductionCode();
// then
assertThat(TEST_LOGGER.getLoggingEvents()).extracting("level", "message").contains(
tuple(INFO, "info message"),
tuple(ERROR, "error message"),
tuple(ERROR, "error message with exception")
);
}
}
这也有不依赖于Hamcrest匹配器库的优势。
我建议一个简单的,可重用的间谍实现,它可以作为JUnit规则包含在测试中:
public final class LogSpy extends ExternalResource {
private Logger logger;
private ListAppender<ILoggingEvent> appender;
@Override
protected void before() {
appender = new ListAppender<>();
logger = (Logger) LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME); // cast from facade (SLF4J) to implementation class (logback)
logger.addAppender(appender);
appender.start();
}
@Override
protected void after() {
logger.detachAppender(appender);
}
public List<ILoggingEvent> getEvents() {
if (appender == null) {
throw new UnexpectedTestError("LogSpy needs to be annotated with @Rule");
}
return appender.list;
}
}
在您的测试中,您将通过以下方式激活间谍:
@Rule
public LogSpy log = new LogSpy();
调用log.getEvents()
(或其他自定义方法)来检查记录的事件。
一个简单的解决方案可能是用Mockito模拟appender(例如)
@Slf4j
class MyClass {
public void doSomething() {
log.info("I'm on it!");
}
}
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.containsString;
import static org.hamcrest.Matchers.is;
import static org.mockito.Mockito.verify;
@RunWith(MockitoJUnitRunner.class)
public class MyClassTest {
@Mock private Appender<ILoggingEvent> mockAppender;
private MyClass sut = new MyClass();
@Before
public void setUp() {
Logger logger = (Logger) LoggerFactory.getLogger(MyClass.class.getName());
logger.addAppender(mockAppender);
}
@Test
public void shouldLogInCaseOfError() {
sut.doSomething();
verify(mockAppender).doAppend(ArgumentMatchers.argThat(argument -> {
assertThat(argument.getMessage(), containsString("I'm on it!"));
assertThat(argument.getLevel(), is(Level.INFO));
return true;
}));
}
}
注意:我使用断言而不是返回false
作为生成代码和(可能)错误更容易阅读但如果您有多个验证它将无法工作。在这种情况下,您需要返回布尔值,指示值是否符合预期。