cmd/go: timeout in TestCache* on darwin-amd64-10_12

[bcmills]

From darwin-amd64-10_12 (https://build.golang.org/log/9f4a33126668c564bf4bddb208bc9c6af1b7d149):

panic: test timed out after 9m0s
[…]
goroutine 657 [syscall]:
syscall.syscall6(0x10af9b0, 0x5204, 0xc00046ecb4, 0x0, 0xc0003945a0, 0x0, 0x0, 0x0, 0x0, 0x0)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/runtime/sys_darwin.go:74 +0x2e
syscall.wait4(0x5204, 0xc00046ecb4, 0x0, 0xc0003945a0, 0x90, 0x16e5c00, 0x1)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/syscall/zsyscall_darwin_amd64.go:44 +0x87
syscall.Wait4(0x5204, 0xc00046ed04, 0x0, 0xc0003945a0, 0x1c041a0, 0x1, 0x1d42b28)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/syscall/syscall_bsd.go:129 +0x51
os.(*Process).wait(0xc000504240, 0x17582e0, 0x17582e8, 0x17582d8)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/os/exec_unix.go:38 +0x7b
os.(*Process).Wait(...)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/os/exec.go:125
os/exec.(*Cmd).Wait(0xc000434580, 0x0, 0x0)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/os/exec/exec.go:501 +0x60
os/exec.(*Cmd).Run(0xc000434580, 0x6d, 0xc00041a460)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/os/exec/exec.go:341 +0x5c
cmd/go_test.(*testgoData).doRun(0xc0003a2d80, 0xc00041a460, 0x5, 0x5, 0xc00004bc00, 0x1d42b28)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/cmd/go/go_test.go:484 +0x2b7
cmd/go_test.(*testgoData).run(0xc0003a2d80, 0xc00041a460, 0x5, 0x5)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/cmd/go/go_test.go:500 +0x7d
cmd/go_test.TestCacheCoverage(0xc0000e4c00)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/cmd/go/go_test.go:5277 +0x2c3
testing.tRunner(0xc0000e4c00, 0x1757128)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/testing/testing.go:916 +0xc1
created by testing.(*T).Run
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/testing/testing.go:967 +0x351
[…]
goroutine 679 [syscall]:
syscall.syscall6(0x10af9b0, 0x5266, 0xc00060d964, 0x0, 0xc0004b0480, 0x0, 0x0, 0x0, 0x0, 0x0)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/runtime/sys_darwin.go:74 +0x2e
syscall.wait4(0x5266, 0xc00060d964, 0x0, 0xc0004b0480, 0x90, 0x16e5c00, 0x1)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/syscall/zsyscall_darwin_amd64.go:44 +0x87
syscall.Wait4(0x5266, 0xc00060d9b4, 0x0, 0xc0004b0480, 0x1c041a0, 0x1, 0x1d42460)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/syscall/syscall_bsd.go:129 +0x51
os.(*Process).wait(0xc00002c690, 0x17582e0, 0x17582e8, 0x17582d8)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/os/exec_unix.go:38 +0x7b
os.(*Process).Wait(...)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/os/exec.go:125
os/exec.(*Cmd).Wait(0xc00054c840, 0x0, 0x0)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/os/exec/exec.go:501 +0x60
os/exec.(*Cmd).Run(0xc00054c840, 0x6d, 0xc0000f9740)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/os/exec/exec.go:341 +0x5c
cmd/go_test.(*testgoData).doRun(0xc0003a3200, 0xc0000f9740, 0x3, 0x3, 0xc0002ae400, 0x1d42460)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/cmd/go/go_test.go:484 +0x2b7
cmd/go_test.(*testgoData).run(0xc0003a3200, 0xc0000f9740, 0x3, 0x3)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/cmd/go/go_test.go:500 +0x7d
cmd/go_test.TestTestCacheInputs(0xc0000e5200)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/cmd/go/go_test.go:5607 +0x2378
testing.tRunner(0xc0000e5200, 0x17577f0)
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/testing/testing.go:916 +0xc1
created by testing.(*T).Run
	/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/go/src/testing/testing.go:967 +0x351

It's not obvious to me whether this is due to a bug in cmd/go or the same underlying platform issue as #25696.

CC @jayconrod @ianlancetaylor

[ianlancetaylor]

The stack trace just shows the test program waiting for the invocation of go test -cover -short math strings to complete. I guess we should put a timeout on the execution of the subprogram. Maybe we could use the new t.Deadline in testgoData.doRun. Or rewrite the test to be a script test.

[bcmills]

Rewriting to a script test sounds like a great idea — we already set a timeout in those.