The plugin does not set sourcepath for test scope classes correctly

[TeofilisMartisius]

The plugin does not set sourcepath for test scope java files correctly.

This results in spotbugs using relative file names for the test java sources, which results in filters that rely on directories where source files are located (like generated-test-classes) failing.

One character change to fix this in the PR here: #1090

[hazendaz]

resolved with #1090