go test -v -p 1 -count 1 ./foo...
And compare to
go test -v p 2 -count 1 ./foo...
And compare to
go test -v -p 10 -count 1 ./foo...
time go test -p 1 -count 1 ./foo...
time go test -p 2 -count 1 ./foo...
time go test -p 10 -count 1 ./foo...
should give
ok github.com/cybozu-private/test-go-test/foo 5.104s
ok github.com/cybozu-private/test-go-test/foo/bar 5.110s
ok github.com/cybozu-private/test-go-test/foo/baz 5.112s
? github.com/cybozu-private/test-go-test/foo/utils [no test files]
go test -p 1 -count 1 ./foo... 0.29s user 0.22s system 3% cpu 16.003 total
ok github.com/cybozu-private/test-go-test/foo 5.230s
ok github.com/cybozu-private/test-go-test/foo/bar 5.370s
? github.com/cybozu-private/test-go-test/foo/utils [no test files]
ok github.com/cybozu-private/test-go-test/foo/baz 5.232s
go test -p 2 -count 1 ./foo... 0.28s user 0.22s system 4% cpu 10.888 total
? github.com/cybozu-private/test-go-test/foo/utils [no test files]
ok github.com/cybozu-private/test-go-test/foo 5.093s
ok github.com/cybozu-private/test-go-test/foo/bar 5.135s
ok github.com/cybozu-private/test-go-test/foo/baz 5.183s
go test -p 10 -count 1 ./foo... 0.33s user 0.30s system 11% cpu 5.447 tota