<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def coverage(reportdir=None, extra=None):
 """Test this project with coverage reports"""


    import coverage as coverage_api
    cov = coverage_api.coverage()
    opts = {'directory': reportdir} if reportdir else {}

    cov.start()
    test(extra)
    cov.stop()
    cov.html_report(**opts)