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cmd/cover: go test -cover and go tool cover -func don't give the same results #20515

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dlespiau opened this issue May 28, 2017 · 2 comments
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cmd/cover: go test -cover and go tool cover -func don't give the same results #20515

dlespiau opened this issue May 28, 2017 · 2 comments
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@dlespiau
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What version of Go are you using (go version)?

go version go1.8 linux/amd64

What did you do?

I used the github.com/dlespiau/x86db package for the example below, but the same issue can be reproduced on other packages I have around and so assuming it's a general problem:

$ go test -coverprofile=profile.cov
PASS
coverage: 26.3% of statements

Whereas:

$ go tool cover -func=profile.cov | tail -1
total:							(statements)		26.1%

Not that I've noticed larger differences, up to 1% on other packages.

What did you expect to see?

I expect to see the same coverage number.

What did you see instead?

Two different coverage percentages.
@ALTree ALTree changed the title go test -cover and go tool cover -func don't give the same results cmd/cover: go test -cover and go tool cover -func don't give the same results May 28, 2017
@ALTree ALTree added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label May 28, 2017
@gopherbot
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CL https://golang.org/cl/44337 mentions this issue.

@JayNakrani
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JayNakrani commented May 28, 2017 •
edited

Found the issue.

cmd/cover/func.go initializes total to 1 for each function. Whereas testing/cover.go only does it once. So if your code has lots of functions with total==0, then discrepancy is going to be high.

http://golang.org/cl/44337 should fix that.

@JayNakrani JayNakrani added this to the Go1.9Maybe milestone May 28, 2017
@JayNakrani JayNakrani removed the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label May 28, 2017
dlespiau pushed a commit to dlespiau/covertool that referenced this issue May 29, 2017
coverage: Add a coverage command
4bc0b9d 
This command computes the coverage percentage of the whole profile.

This is different from what go tool cover -func does because of this
bug: golang/go#20515

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
@golang golang locked and limited conversation to collaborators Jun 2, 2018
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