"coverage combine" should error if no coverage

[nedbat]

Originally reported by meejah (Bitbucket: meejah, GitHub: meejah)

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If you run "coverage combine" and there is no .coverage file (or .coverage.* files) it will run without error and produce a .coverage that is "empty" (i.e. has the comment and then an empty dict).

It seems more intuitive that it should be an error to try and combine nothing.

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• Bitbucket: https://bitbucket.org/ned/coveragepy/issue/412

[nedbat]

It's simple enough to make the command fail, by making Coverage.combine() raise an exception, but the nose coverage plugin calls combine early on, and it will stop working if I do this.

A little more thought...

[nedbat]

Original comment by John Vandenberg (Bitbucket: jayvdb, GitHub: jayvdb)

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A more specific case of this is https://bitbucket.org/ned/coveragepy/issues/516/running-coverage-combine-twice-deletes-all

[nedbat]

Fixed in 34ae57c51cfb (bb), it would be great if you could test it out for me.

[nedbat]

This fix was released as part of Coverage.py 4.3.