wip: prepare test cases

go.mod

@@ -10,6 +10,7 @@ require (
 )
 
 require (
+	github.com/google/go-cmp v0.6.0 // indirect
 	github.com/kr/pretty v0.1.0 // indirect
 	gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 // indirect
 )

go.sum

@@ -1,3 +1,5 @@
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/gorilla/websocket v1.4.1 h1:q7AeDBpnBk8AogcD4DSag/Ukw/KV+YhzLj2bP5HvKCM=
 github.com/gorilla/websocket v1.4.1/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
 github.com/haya14busa/go-checkstyle v0.0.0-20170303121022-5e9d09f51fa1/go.mod h1:RsN5RGgVYeXpcXNtWyztD5VIe7VNSEqpJvF2iEH7QvI=

langserver/diff_test.go

@@ -0,0 +1,61 @@
+package langserver_test
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/mattn/efm-langserver/langserver"
+)
+
+func TestComputeEdits(t *testing.T) {
+	cases := []struct {
+		name          string
+		before, after string
+		want          []langserver.TextEdit
+	}{
+		{
+			name:   "Empty",
+			before: "", after: "", want: []langserver.TextEdit{},
+		},
+		{
+			name:   "Empty to one line",
+			before: "", after: "foo", want: []langserver.TextEdit{
+				{NewText: "foo"},
+			},
+		},
+		{
+			name:   "One line to another",
+			before: "foo", after: "bar", want: []langserver.TextEdit{
+				{Range: langserver.Range{End: langserver.Position{Line: 1}}},
+				{Range: langserver.Range{Start: langserver.Position{Line: 1}, End: langserver.Position{Line: 1}}, NewText: "bar"},
+			},
+		},
+		{
+			name:   "Replace multi lines (issue 281)",
+			before: "foo\nbar\nbaz\n", after: "one\ntwo\nthree\n",
+			want: []langserver.TextEdit{
+				{Range: langserver.Range{End: langserver.Position{Line: 3}}},
+				{
+					Range:   langserver.Range{Start: langserver.Position{Line: 3}, End: langserver.Position{Line: 3}},
+					NewText: "three\n",
+				},
+				{
+					Range:   langserver.Range{Start: langserver.Position{Line: 3}, End: langserver.Position{Line: 3}},
+					NewText: "two\n",
+				},
+				{
+					Range:   langserver.Range{Start: langserver.Position{Line: 3}, End: langserver.Position{Line: 3}},
+					NewText: "one\n",
+				},
+			},
+		},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			edits := langserver.ComputeEdits("", c.before, c.after)
+			if diff := cmp.Diff(c.want, edits); diff != "" {
+				t.Errorf("unexpected edits (-want +got):\n%s", diff)
+			}
+		})
+	}
+}