cmd/go: add '-skip' to list of cacheable test flags

-run is cacheable, so -skip should be cacheable too.

Fixes #70692

Change-Id: I16880189b0d3a963f8f08008fc7fedcdc6f11630
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest,gotip-windows-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/go/+/646997
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Sam Thanawalla <[email protected]>

Author: matloob

src/cmd/go/alldocs.go

@@ -127,7 +127,7 @@ elapsed time in the summary line.
 The rule for a match in the cache is that the run involves the same
 test binary and the flags on the command line come entirely from a
 restricted set of 'cacheable' test flags, defined as -benchtime, -cpu,
--list, -parallel, -run, -short, -timeout, -failfast, -fullpath and -v.
+-list, -parallel, -run, -short, -skip, -timeout, -failfast, -fullpath and -v.
 If a run of go test has any test or non-test flags outside this set,
 the result is not cached. To disable test caching, use any test flag
 or argument other than the cacheable flags. The idiomatic way to disable
@@ -1781,6 +1781,7 @@ func (c *runCache) tryCacheWithID(b *work.Builder, a *work.Action, id string) bo
 			"-test.parallel",
 			"-test.run",
 			"-test.short",
+			"-test.skip",
 			"-test.timeout",
 			"-test.failfast",
 			"-test.v",

src/cmd/go/internal/test/test.go

@@ -128,6 +128,11 @@ go test testcache -run=TestOSArgs -fullpath
 go test testcache -run=TestOSArgs -fullpath
 stdout '\(cached\)'
 
+# golang.org/issue/70692: that includes the `-skip` flag
+go test testcache -run=TestOdd -skip=TestOddFile
+! stdout '\(cached\)'
+go test testcache -run=TestOdd -skip=TestOddFile
+stdout '\(cached\)'
 
 # Executables within GOROOT and GOPATH should affect caching,
 # even if the test does not stat them explicitly.