Maven surefire fails on install but not on package phase with NoClassDefFoundError

Question

I've got a strage problem.
When I build my maven project like this:
mvn clean package it compiles and successfully runs the unit tests but when I do
mvn clean install it still compiles, reports build success but shows this strange error:

java.lang.NoClassDefFoundError: com/foo/BarClass
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
    at com.foo.BarTest.shouldTestSomething(BarTest.java:35)

I've got maven 3.0.4, surefire-plugin-version 2.14, junit 4.11 Here are representative parts of my pom.xml

<build>
        <pluginManagement>
            <plugins>               
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-surefire-plugin</artifactId>
                    <version>2.14</version>
                </plugin>
         </pluginManagement>
</build>
<dependencies>
<dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>
</dependencies>

I've played with changing surefire/junit versions as well with surefire's <useSystemClassLoader>false</useSystemClassLoader> but still got the problem.
I really don't understand the cause of the NoClassDefFound error ... Can you please help me?

Answer 1

So finally I fixed the messy problem:
I also had cobertura plugin running (like any quality software project has :), that instrumented the classes thus triggering a recompile, thus a re-run of unit-tests hence the strange NoClassDefError
Huh, what a busy day!