Branch coverage does weird things for yield statements

[nedbat]

Originally reported by Tristan Seligmann (Bitbucket: mithrandi, GitHub: mithrandi)

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Consider this example:

def gen(): 
    print 'hi mom!' 
    yield 42 
    print 'not covered' 
print gen().next() 

If I run it without --branch, coverage tells me the first print and yield are executed, but the third print isn't; all as expected.

If I run it with --branch, coverage tells me the first print was executed, but that the yield was not executed at all. Huh?

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• Bitbucket: https://bitbucket.org/ned/coveragepy/issue/482

[nedbat]

Original comment by Pi Delport (Bitbucket: pjdelport, GitHub: pjdelport)

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This makes partial sense: the yield is an expression that branches control flow, and doesn't actually fully cover the line until control is resumed back into the generator. For example, consider:

def gen():
    print('hi mom!')
    print((yield 42), 1 / 0)
    print('not covered')

print gen().next()

However, that doesn't explain why it counts the yield line as completely missed instead of partial.

[nedbat]

Duplicate of #440.