cmd/go/internal/test: add 'tests' vet check to 'go test' suite

The tests analyser reports structural problems in test
declarations. Presumably most of these would be caught by
go test itself, which compiles and runs (some subset of) the
tests, but Benchmark and Fuzz functions are executed less
frequently and may benefit more from static checks.

Also, reflect the change in go test help message.

+ release note

Fixes golang/go#44251

Change-Id: If5b9dee6d18fa0bc4de7f5f5f549eddeae953fc2
Reviewed-on: https://go-review.googlesource.com/c/go/+/529816
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Alan Donovan <adonovan@google.com>

doc/next/3-tools.md

@@ -10,3 +10,12 @@ or copying the `go` binary.
 
 ### Cgo {#cgo}
 
+### Vet
+
+The new `tests` analyzer reports common mistakes in declarations of
+tests, fuzzers, benchmarks, and examples in test packages, such as
+malformed names, wrong signatures, or examples that document
+non-existent identifiers. Some of these mistakes may cause tests not
+to run.
+
+This analyzer is among the subset of analyzers that are run by `go test`.

src/cmd/go/alldocs.go

@@ -1756,7 +1756,7 @@
 // finds any problems, go test reports those and does not run the test
 // binary. Only a high-confidence subset of the default go vet checks are
 // used. That subset is: atomic, bool, buildtags, directive, errorsas,
-// ifaceassert, nilfunc, printf, and stringintconv. You can see
+// ifaceassert, nilfunc, printf, stringintconv, and tests. You can see
 // the documentation for these and other vet tests via "go doc cmd/vet".
 // To disable the running of go vet, use the -vet=off flag. To run all
 // checks, use the -vet=all flag.

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

@@ -79,7 +79,7 @@ and its test source files to identify significant problems. If go vet
 finds any problems, go test reports those and does not run the test
 binary. Only a high-confidence subset of the default go vet checks are
 used. That subset is: atomic, bool, buildtags, directive, errorsas,
-ifaceassert, nilfunc, printf, and stringintconv. You can see
+ifaceassert, nilfunc, printf, stringintconv, and tests. You can see
 the documentation for these and other vet tests via "go doc cmd/vet".
 To disable the running of go vet, use the -vet=off flag. To run all
 checks, use the -vet=all flag.
@@ -667,7 +667,7 @@ var defaultVetFlags = []string{
 	"-slog",
 	"-stringintconv",
 	// "-structtags",
-	// "-tests",
+	"-tests",
 	// "-unreachable",
 	// "-unsafeptr",
 	// "-unusedresult",

src/cmd/go/testdata/script/test_bad_example.txt

@@ -1,6 +1,7 @@
 # Tests that invalid examples are ignored.
 # Verifies golang.org/issue/35284
-go test x_test.go
+# Disable vet, as 'tests' analyzer objects to surplus parameter.
+go test -vet=off x_test.go
 
 -- x_test.go --
 package  x
@@ -10,4 +11,4 @@ import "fmt"
 func ExampleThisShouldNotHaveAParameter(thisShouldntExist int) {
 	fmt.Println("X")
 	// Output:
-}
+}