cmd/cgo: more expansive test coverage

[mdempsky]

cgo is very subtle, yet it's lacking in test coverage. For example, misc/cgo/test doesn't have any tests for C.enum_foo or C.struct_bar, and misc/cgo/testgodefs doesn't have any tests for constants (to be addressed by CL 237558).

/cc @ianlancetaylor

[howjmay]

I want to try to take this issue.
For the first step, I want to implement the test for enum_foo.
Should I add an extra file, test_enum.go, for testing?

[ianlancetaylor]

Ideally the test should be added to the existing files misc/cgo/test/test.go and/or misc/cgo/test/testx.go. Thanks.

[gopherbot]

Change https://golang.org/cl/240697 mentions this issue: cgo: Test Allocating C enum with C.enum_*

[howjmay]

Should I add some tests for union as well?

[ianlancetaylor]

@howjmay Sure. Thanks.

[gopherbot]

Change https://golang.org/cl/246057 mentions this issue: cmd/cgo: fix mangling of enum and union types

[gopherbot]

Change https://golang.org/cl/248683 mentions this issue: misc/cgo: Add test for C union read/write