add patch modifier struct

pkg/git/patch_modifier_test.go

@@ -0,0 +1,68 @@
+package git
+
+import (
+	"io/ioutil"
+	"testing"
+
+	"github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+)
+
+func newDummyLog() *logrus.Entry {
+	log := logrus.New()
+	log.Out = ioutil.Discard
+	return log.WithField("test", "test")
+}
+
+func newDummyPatchModifier() *PatchModifier {
+	return &PatchModifier{
+		Log: newDummyLog(),
+	}
+}
+func TestModifyPatch(t *testing.T) {
+	type scenario struct {
+		testName              string
+		patchFilename         string
+		lineNumber            int
+		shouldError           bool
+		expectedPatchFilename string
+	}
+
+	scenarios := []scenario{
+		{
+			"Removing one line",
+			"testdata/testPatchBefore.diff",
+			8,
+			false,
+			"testdata/testPatchAfter1.diff",
+		},
+		{
+			"Adding one line",
+			"testdata/testPatchBefore.diff",
+			10,
+			false,
+			"testdata/testPatchAfter2.diff",
+		},
+	}
+
+	for _, s := range scenarios {
+		t.Run(s.testName, func(t *testing.T) {
+			p := newDummyPatchModifier()
+			beforePatch, err := ioutil.ReadFile(s.patchFilename)
+			if err != nil {
+				panic("Cannot open file at " + s.patchFilename)
+			}
+			afterPatch, err := p.ModifyPatch(string(beforePatch), s.lineNumber)
+			if s.shouldError {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+				expected, err := ioutil.ReadFile(s.expectedPatchFilename)
+				if err != nil {
+					panic("Cannot open file at " + s.expectedPatchFilename)
+				}
+				assert.Equal(t, string(expected), afterPatch)
+			}
+		})
+	}
+}