Some refactor on git diff and ignore getting commit information failed on migrating pull request review comments (#9996)

* Some refactor on git diff and ignore getting commit information failed on migrating pull request review comments

* fix test

* fix lint

* Change error log to warn

modules/git/diff_test.go

@@ -0,0 +1,82 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package git
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+const exampleDiff = `diff --git a/README.md b/README.md
+--- a/README.md
++++ b/README.md
+@@ -1,3 +1,6 @@
+ # gitea-github-migrator
++
++ Build Status
+- Latest Release
+ Docker Pulls
++ cut off
++ cut off`
+
+func TestCutDiffAroundLine(t *testing.T) {
+	result := CutDiffAroundLine(strings.NewReader(exampleDiff), 4, false, 3)
+	resultByLine := strings.Split(result, "\n")
+	assert.Len(t, resultByLine, 7)
+	// Check if headers got transferred
+	assert.Equal(t, "diff --git a/README.md b/README.md", resultByLine[0])
+	assert.Equal(t, "--- a/README.md", resultByLine[1])
+	assert.Equal(t, "+++ b/README.md", resultByLine[2])
+	// Check if hunk header is calculated correctly
+	assert.Equal(t, "@@ -2,2 +3,2 @@", resultByLine[3])
+	// Check if line got transferred
+	assert.Equal(t, "+ Build Status", resultByLine[4])
+
+	// Must be same result as before since old line 3 == new line 5
+	newResult := CutDiffAroundLine(strings.NewReader(exampleDiff), 3, true, 3)
+	assert.Equal(t, result, newResult, "Must be same result as before since old line 3 == new line 5")
+
+	newResult = CutDiffAroundLine(strings.NewReader(exampleDiff), 6, false, 300)
+	assert.Equal(t, exampleDiff, newResult)
+
+	emptyResult := CutDiffAroundLine(strings.NewReader(exampleDiff), 6, false, 0)
+	assert.Empty(t, emptyResult)
+
+	// Line is out of scope
+	emptyResult = CutDiffAroundLine(strings.NewReader(exampleDiff), 434, false, 0)
+	assert.Empty(t, emptyResult)
+}
+
+func BenchmarkCutDiffAroundLine(b *testing.B) {
+	for n := 0; n < b.N; n++ {
+		CutDiffAroundLine(strings.NewReader(exampleDiff), 3, true, 3)
+	}
+}
+
+func ExampleCutDiffAroundLine() {
+	const diff = `diff --git a/README.md b/README.md
+--- a/README.md
++++ b/README.md
+@@ -1,3 +1,6 @@
+ # gitea-github-migrator
++
++ Build Status
+- Latest Release
+ Docker Pulls
++ cut off
++ cut off`
+	result := CutDiffAroundLine(strings.NewReader(diff), 4, false, 3)
+	println(result)
+}
+
+func TestParseDiffHunkString(t *testing.T) {
+	leftLine, leftHunk, rightLine, rightHunk := ParseDiffHunkString("@@ -19,3 +19,5 @@ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER")
+	assert.EqualValues(t, 19, leftLine)
+	assert.EqualValues(t, 3, leftHunk)
+	assert.EqualValues(t, 19, rightLine)
+	assert.EqualValues(t, 5, rightHunk)
+}