Expecting Log Output

Sometimes you will need to test for content of log output. For instance, you are testing some service deep inside the stack and do not have a direct access to it.

Configure a Log4j Logger

Create a log4j.properties file (presuming a Maven file structure):

 src
  +--test
      +--resources
             +--log4j.properties

with the following content:

log4j.rootLogger=INFO,CONSOLE
log4j.appender.CONSOLE=org.javalite.logging.LoggingTestAppender

This logger simply drops everything in STDIO.

Maven will place the src/test/resources at the top of the classpath for tests but will not package into the final artifact, so your real Log4j configuration is safe.

Writing a spec

@Test
public void shouldExpectFoo() {
    SystemStreamUtil.replaceOut();
    //some code here to cause actual actions
    String out = SystemStreamUtil.getSystemOut();
    String[] lines = Util.split(out, System.getProperty("line.separator"));
    the(lines[4]).shouldContain("select * from people");
    SystemStreamUtil.restoreSystemOut();
 }

• Line 3: will start intercepting and accumulating all output to System.out.
  
• Line 5: get all log output as a single String object
• Line 6: splitting the log output into individual log lines
• Line 7: asserting the value in a specific line
• Line 8: restorin the STDIO back to its natural state for all other tests that follow.

STDERR?

The same technique can be done with SystemStreamUtil.getSystemErr() and SystemStreamUtil.restoreSystemErr() respectively.

Do not forget to restore the STDIO or STDERR output, otherwise you will not see much of log output.