add initial support for running tests

For now, it mainly consists of not garbling Test* funcs, and not
garbling the _testmain.go file that will run them.

Updates #6.

main.go

@@ -108,7 +108,7 @@ func main1() int {
 func mainErr(args []string) error {
 	// If we recognise an argument, we're not running within -toolexec.
 	switch cmd := args[0]; cmd {
-	case "build":
+	case "build", "test":
 		execPath, err := os.Executable()
 		if err != nil {
 			return err
@@ -192,6 +192,9 @@ func transformCompile(args []string) ([]string, error) {
 		// Nothing to transform; probably just ["-V=full"].
 		return args, nil
 	}
+	if len(paths) == 1 && filepath.Base(paths[0]) == "_testmain.go" {
+		return args, nil
+	}
 
 	// If the value of -trimpath doesn't contain the separator ';', the 'go
 	// build' command is most likely not using '-trimpath'.
@@ -363,6 +366,9 @@ func transformGo(node ast.Node, info *types.Info) ast.Node {
 				case "main", "init":
 					return true // don't break them
 				}
+				if strings.HasPrefix(node.Name, "Test") && isTestSignature(sign) {
+					return true // don't break tests
+				}
 			case nil:
 				switch cursor.Parent().(type) {
 				case *ast.AssignStmt:
@@ -404,6 +410,27 @@ func isStandardLibrary(path string) bool {
 	return !strings.Contains(path, ".")
 }
 
+// isTestSignature returns true if the signature matches "func _(*testing.T)".
+func isTestSignature(sign *types.Signature) bool {
+	if sign.Recv() != nil {
+		return false
+	}
+	params := sign.Params()
+	if params.Len() != 1 {
+		return false
+	}
+	ptr, ok := params.At(0).Type().(*types.Pointer) // *testing.T
+	if !ok {
+		return false
+	}
+	named, ok := ptr.Elem().(*types.Named) // testing.T
+	if !ok {
+		return false
+	}
+	obj := named.Obj()
+	return obj.Pkg().Path() == "testing" && obj.Name() == "T"
+}
+
 func transformLink(args []string) ([]string, error) {
 	flags, paths := splitFlagsFromFiles(args, ".a")
 	if len(paths) == 0 {

testdata/scripts/test.txt

@@ -0,0 +1,40 @@
+! garble badcmd
+stderr 'unknown command'
+
+! garble /does/not/exist
+stderr 'unknown tool'
+
+! garble /does/not/exist/compile
+stderr 'no such file'
+
+exec go test -v
+stdout 'PASS.*TestFoo'
+
+garble test -v
+stdout 'PASS.*TestFoo'
+
+garble test -c -vet=off
+bingrep bar.test$exe 'TestFoo'
+! bingrep bar.test$exe 'ImportedVar'
+
+-- go.mod --
+module foo.com/bar
+-- bar.go --
+package bar
+
+func Foo() string { return "Foo" }
+
+var ImportedVar = "imported var value"
+-- bar_test.go --
+package bar
+
+import (
+	"testing"
+)
+
+func TestFoo(t *testing.T) {
+	t.Log(ImportedVar)
+	if Foo() != "Foo" {
+		t.FailNow()
+	}
+}