1 files changed, 57 insertions, 0 deletions
diff --git a/gopls/internal/lsp/mod/mod_test.go b/gopls/internal/lsp/mod/mod_test.go
new file mode 100644
index 000000000..c2aa1af6f
--- /dev/null
+++ b/gopls/internal/lsp/mod/mod_test.go
@@ -0,0 +1,57 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package mod
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"golang.org/x/tools/gopls/internal/lsp/cache"
+	"golang.org/x/tools/gopls/internal/lsp/source"
+	"golang.org/x/tools/gopls/internal/lsp/tests"
+	"golang.org/x/tools/gopls/internal/span"
+	"golang.org/x/tools/internal/testenv"
+)
+
+func TestMain(m *testing.M) {
+	testenv.ExitIfSmallMachine()
+	os.Exit(m.Run())
+}
+
+func TestModfileRemainsUnchanged(t *testing.T) {
+	ctx := tests.Context(t)
+	session := cache.NewSession(ctx, cache.New(nil), nil)
+	options := source.DefaultOptions().Clone()
+	tests.DefaultOptions(options)
+	options.TempModfile = true
+	options.Env = map[string]string{"GOPACKAGESDRIVER": "off", "GOROOT": ""}
+
+	// Make sure to copy the test directory to a temporary directory so we do not
+	// modify the test code or add go.sum files when we run the tests.
+	folder, err := tests.CopyFolderToTempDir(filepath.Join("testdata", "unchanged"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(folder)
+
+	before, err := ioutil.ReadFile(filepath.Join(folder, "go.mod"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, _, release, err := session.NewView(ctx, "diagnostics_test", span.URIFromPath(folder), options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	release()
+	after, err := ioutil.ReadFile(filepath.Join(folder, "go.mod"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(before) != string(after) {
+		t.Errorf("the real go.mod file was changed even when tempModfile=true")
+	}
+}