ThreadsafeForwardingResult leaks tags

[Jonathan Lange]

tags set in one test are local to that test. Tests that follow should know nothing about tags set in previous tests. However, once a test-local tag is set in ThreadsafeForwardingResult, that tag is set for all tests that follow.

  tsfr = ThreadsafeForwardingResult(result)
  tsfr.startTest(a)
  tsfr.tags(x, y)
  tsfr.addSuccess(a)
  tsfr.stopTest(a)
  tsfr.startTest(b)
  tsfr.addSuccess(b)
  tsfr.stopTest(b)

And 'result' receives:

  startTest(a)
  tags(x, y)
  addSuccess(a)
  stopTest(a)
  startTest(b)
  tags(x, y)
  addSuccess(b)
  stopTest(b)

Whereas it should receive:

  startTest(a)
  tags(x, y)
  addSuccess(a)
  stopTest(a)
  startTest(b)
  addSuccess(b)
  stopTest(b)