Testing polar chart:

Since the tests typically initialize the chart once for the whole test case,
it is difficult to test the components against polar chart unless all tests
are duplicated or massively refactored. Neither option is desirable, so instead
we check environment variable TEST_POLAR_CHART. If it is not empty, we run
the tests that are relevant for polar chart against polar chart. Unfortunately
This means two runs of the tests with different environment are required for
full coverage.