cmd/go: add test code packages in list -test

Previously go list -test <pkg> would return pkg and, if it exists,
pkg.test, the test main package. This change will also list the
two test code packages (if they exist) that contain testing functions,
<pkg> [<pkg>.test] and <pkg>_test [<pkg>.test].

These packages which contain testing code are usually the packages
go list users desire to know about, so they should be surfaced
in go list -test.

See the discussion at
golang.org/cl/123635#message-5befbc66663063fb7247645a02ab1327a681e362
for more context.

Change-Id: I7170b539d02b548c050ac54048735ed785f47389
Reviewed-on: https://go-review.googlesource.com/126475
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/go_test.go

@@ -1757,7 +1757,7 @@ func TestGoListTest(t *testing.T) {
 	tg.run("list", "-test", "sort")
 	tg.grepStdout(`^sort.test$`, "missing test main")
 	tg.grepStdout(`^sort$`, "missing real sort")
-	tg.grepStdoutNot(`^sort \[sort.test\]$`, "unexpected test copy of sort")
+	tg.grepStdout(`^sort \[sort.test\]$`, "unexpected test copy of sort")
 	tg.grepStdoutNot(`^testing \[sort.test\]$`, "unexpected test copy of testing")
 	tg.grepStdoutNot(`^testing$`, "unexpected real copy of testing")
 

src/cmd/go/internal/list/list.go

@@ -424,7 +424,7 @@ func runList(cmd *base.Command, args []string) {
 				continue
 			}
 			if len(p.TestGoFiles)+len(p.XTestGoFiles) > 0 {
-				pmain, _, _, err := load.TestPackagesFor(p, nil)
+				pmain, ptest, pxtest, err := load.TestPackagesFor(p, nil)
 				if err != nil {
 					if *listE {
 						pkgs = append(pkgs, &load.Package{
@@ -439,6 +439,12 @@ func runList(cmd *base.Command, args []string) {
 					continue
 				}
 				pkgs = append(pkgs, pmain)
+				if ptest != nil {
+					pkgs = append(pkgs, ptest)
+				}
+				if pxtest != nil {
+					pkgs = append(pkgs, pxtest)
+				}
 
 				data := *pmain.Internal.TestmainGo
 				h := cache.NewHash("testmain")