cmd/go: use local loader state in test

This change converts the import test to use a local module loader
state variable, instead of the dependency on global state.

This commit is part of the overall effort to eliminate global
modloader state.

Change-Id: I5687090c160bf64ce36356768f7cf74333fab724
Reviewed-on: https://go-review.googlesource.com/c/go/+/711138
Reviewed-by: Michael Matloob <matloob@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: jitsu-net

src/cmd/go/internal/modload/import_test.go

@@ -56,25 +56,25 @@ var importTests = []struct {
 }
 
 func TestQueryImport(t *testing.T) {
+	loaderstate := NewState()
+	loaderstate.RootMode = NoRoot
+
 	testenv.MustHaveExternalNetwork(t)
 	testenv.MustHaveExecPath(t, "git")
 
 	oldAllowMissingModuleImports := allowMissingModuleImports
-	oldRootMode := LoaderState.RootMode
 	defer func() {
 		allowMissingModuleImports = oldAllowMissingModuleImports
-		LoaderState.RootMode = oldRootMode
 	}()
 	allowMissingModuleImports = true
-	LoaderState.RootMode = NoRoot
 
 	ctx := context.Background()
-	rs := LoadModFile(LoaderState, ctx)
+	rs := LoadModFile(loaderstate, ctx)
 
 	for _, tt := range importTests {
 		t.Run(strings.ReplaceAll(tt.path, "/", "_"), func(t *testing.T) {
 			// Note that there is no build list, so Import should always fail.
-			m, err := queryImport(LoaderState, ctx, tt.path, rs)
+			m, err := queryImport(loaderstate, ctx, tt.path, rs)
 
 			if tt.err == "" {
 				if err != nil {