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The option -o can be added when you are running without an internet connection.
Netbeans Settings
To fix running Maven TestCases in Netbeans, right-click on the project and go to Properties > Build. Click on Compile. Set Compile on Save to For application execution only.
Increase the VM heap size for the project by going to the project's Properties and under VM Options in Run, put in -Xmx1024m or however much memory is appropriate for your system. The default is usually -Xmx512, which may not be enough for running some tests.