Most lifecycles bind the test goal of the Surefire plugin to the test phase. The Surefire plugin is Maven's unit testing plugin, the default behavior of Surefire is to look for all classes ending in *Test in the test source directory and to run them as JUnit tests. The Surefire plugin can also be configured to run TestNG unit tests.

After running mvn test, you should also notice that the Surefire produces a number of reports in target/surefire-reports. This reports directory will have two files for each test executed by the Surefire plugin: an XML document containing execution information for the test, and a text file containing the output of the unit test. If there is a problem during the test phase and a unit test has failed, you can use the output of Maven and the contents of this directory to track down the cause of a test failure. This surefire-reports/ directory is also used during site generation to create an easy to read summary of all the unit tests in a project.

If you are working on a project that has some failing unit tests, but you want the project to produce output, you'll need to configure the Surefire plugin to continue a build even if it encounters a failure. The default behavior is to stop a build whenever a unit test failure is encountered. To override this behavior, you'll need to set the testFailureIgnore configuration property on the Surefire plugin to true.

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-surefire-plugin</artifactId>
     <configuration>
       <testFailureIgnore>true</testFailureIgnore>
     </configuration>
    </plugin>
    ...
  </plugins>
</build>

If you would like to skip tests altogether, you can do so by executing the following command:

$ mvn install -Dmaven.test.skip=true

The maven.test.skip variable controls both the Compiler and the Surefire plugin, if you pass in maven.test.skip you've told Maven to ignore tests altogether.