Surefire is not picking up Junit 4 tests

I don't know what you mean by "can't execute," but does it help to explicitly set the includes used by the maven-surefire-plugin?

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-surefire-plugin</artifactId>
    <version>2.4.3</version>
    <configuration>
        <includes>
            <include>**/*Test.java</include>
        </includes>
    </configuration>
</plugin>

Also, does running maven with the -X flag provide any useful information?

mvn -X helped me to reveal the following:

...
[INFO] [surefire:test {execution: default-test}]
[DEBUG] dummy:dummy:jar:1.0 (selected for null)
[DEBUG]   org.apache.maven.surefire:surefire-booter:jar:2.4.3:runtime (selected for runtime)
[DEBUG]     org.apache.maven.surefire:surefire-api:jar:2.4.3:runtime (selected for runtime)
[DEBUG] Adding to surefire booter test classpath: /home/mindas/.m2/repository/org/apache/maven/surefire/surefire-booter/2.4.3/surefire-booter-2.4.3.jar
[DEBUG] Adding to surefire booter test classpath: /home/mindas/.m2/repository/org/apache/maven/surefire/surefire-api/2.4.3/surefire-api-2.4.3.jar
[DEBUG] dummy:dummy:jar:1.0 (selected for null)
[DEBUG]   org.testng:testng:jar:jdk15:5.8:test (selected for test)
[DEBUG]     junit:junit:jar:3.8.1:test (selected for test)
[DEBUG] Adding to surefire booter test classpath: /home/mindas/.m2/repository/org/testng/testng/5.8/testng-5.8-jdk15.jar
[DEBUG] Adding to surefire booter test classpath: /home/mindas/.m2/repository/junit/junit/3.8.1/junit-3.8.1.jar
[DEBUG] dummy:dummy:jar:1.0 (selected for null)
[DEBUG] Retrieving parent-POM: org.apache.maven.surefire:surefire-providers:pom:2.4.3 for project: null:surefire-testng:jar:null from the repository.
[DEBUG] Adding managed dependencies for unknown:surefire-testng
[DEBUG]   org.apache.maven.surefire:surefire-api:jar:2.4.3
[DEBUG]   org.apache.maven.surefire:surefire-booter:jar:2.4.3
[DEBUG]   org.codehaus.plexus:plexus-utils:jar:1.5.1
[DEBUG]   org.apache.maven.surefire:surefire-testng:jar:2.4.3:test (selected for test)
[DEBUG]     org.apache.maven:maven-artifact:jar:2.0:test (selected for test)
[DEBUG]       org.codehaus.plexus:plexus-utils:jar:1.0.4:test (selected for test)
[DEBUG]     junit:junit:jar:3.8.1:test (selected for test)
[DEBUG]     org.testng:testng:jar:jdk15:5.7:test (selected for test)
[DEBUG]     org.apache.maven.surefire:surefire-api:jar:2.4.3:test (selected for test)
...
[DEBUG] Test Classpath :
...
[DEBUG]   /home/mindas/.m2/repository/junit/junit/4.7/junit-4.7.jar

So it seems that the problem was coming from testng jar requiring JUnit v3.8.1. Even though Test Classpath was set to depend on JUnit 4, it was too late.

testng dependency was located in my POM:

<dependency>
  <groupId>org.testng</groupId>
  <artifactId>testng</artifactId>
  <version>5.8</version>
  <scope>test</scope>
  <classifier>jdk15</classifier>
</dependency>

Immediately after I have commented it out, tests started to execute.

Lessons learned:

• mvn dependency:tree is not always enough, mvn -X is a friend.
• surefire is not made for developer heaven (I have realized this while looking at project JIRA reports). This is especially true as there are no other alternatives if you use Maven.

Thanks everybody for your help. Unfortunately there is no way to split answer points between Pascal and Kaleb, but Kaleb's advice to use mvn -X helped me to get on the right track so correct answer points go to him.

The Surefire plugin figures out which JUnit provider should be used based upon the classpath. If there are multiple JUnit versions on the classpath, you can either correct the classpath to have only one JUnit version on the classpath (as discussed above), or you can explicitly specify which provider you want to use. For example, specifying the following in your (parent) POM forces using the newest provider (e.g., "surefire-junit47"):

[...]
<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-surefire-plugin</artifactId>
  <version>2.8</version>
  <dependencies>
    <!-- Force using the latest JUnit 47 provider -->
    <dependency>
      <groupId>org.apache.maven.surefire</groupId>
      <artifactId>surefire-junit47</artifactId>
      <version>2.8</version>
    </dependency>
  </dependencies>
[...]

Note however that Surefire 2.7 changed the way it's determining which unit test classes are run. The new behavior when using Surefire 2.7 (or later) with JUnit 4 is that any test without a @Test annotation will be skipped automatically. This may be great if you just have JUnit 4 unit tests, but if you have a combination of JUnit 3 and 4 unit tests, using the "surefire-junit47" provider will not work correctly. In such cases, its best to explicitly choose the "surefire-junit4" provider:

[...]
<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-surefire-plugin</artifactId>
  <version>2.8</version>
  <dependencies>
    <dependency>
      <groupId>org.apache.maven.surefire</groupId>
      <!-- Use the older JUnit 4 provider -->
      <artifactId>surefire-junit4</artifactId>
      <version>2.8</version>
    </dependency>
  </dependencies>
[...]