proposal: go test -c should compile one test binary for all packages listed

[irl-segfault]

Proposal Details

go test -c currently produces one test binary per package listed. When running without -c, go test will run all tests for all packages listed. I propose that go test -c mirror that behavior when compiling a test binary, and produce a single a.out that when executed does exactly the same thing as running go test directly without the -c flag.

The reason that I think this is a good idea is because this behavior would reduce the disparity between using the -c and not using it. Concretely, this would make it easier to build and share test executables to run in a single command. I have a concrete use case for this where we run integration tests in a container that's built on build machines. Enabling this would reduce the image size transferred back and forth :)

[seankhliao]

This looks like an incompatible change in how the go command works.
It also looks infeasible as this would make the test executable built with multiple packages unlike that of one built with a single package, impacting things such as init, who gets the starting thread, which testmain is run, and more generally global resource setup/cleanup/error handling in a way which is likely to break user code.

[bcmills]

This is not feasible in general. Two different packages can each define a test function with the same name, such as Example. How would the -test.run flag distinguish between those functions?

Contrast:

• proposal: testing: fail if the same test function is defined in both the _test and non-_test packages #60977

[irl-segfault]

I was thinking that if go test ./... can successfully run all tests for all packages including cases where there are multiple test functions with the same name, then we could compile a test binary that when executed does exactly same thing. If that's not possible based on the way the go command manages test threads and global resources (or more concretely, existing flags such as -test.run), then I'll close the issue. Thanks for the clarification!