Implemented PR creation in Github driver.

Author: chhsia0

scm/driver/github/pr.go

@@ -51,6 +51,19 @@ func (s *pullService) Close(ctx context.Context, repo string, number int) (*scm.
 	return res, err
 }
 
+func (s *pullService) Create(ctx context.Context, repo string, input *scm.PullRequestInput) (*scm.PullRequest, *scm.Response, error) {
+	path := fmt.Sprintf("repos/%s/pulls", repo)
+	in := &prInput{
+		Title: input.Title,
+		Body:  input.Body,
+		Head:  input.Source,
+		Base:  input.Target,
+	}
+	out := new(pr)
+	res, err := s.client.do(ctx, "POST", path, in, out)
+	return convertPullRequest(out), res, err
+}
+
 type pr struct {
 	Number  int    `json:"number"`
 	State   string `json:"state"`
@@ -85,6 +98,13 @@ type pr struct {
 	UpdatedAt time.Time   `json:"updated_at"`
 }
 
+type prInput struct {
+	Title string `json:"title"`
+	Body  string `json:"body"`
+	Head  string `json:"head"`
+	Base  string `json:"base"`
+}
+
 type file struct {
 	Sha       string `json:"sha"`
 	Filename  string `json:"filename"`

scm/driver/github/pr_test.go

@@ -152,3 +152,40 @@ func TestPullClose(t *testing.T) {
 	t.Run("Request", testRequest(res))
 	t.Run("Rate", testRate(res))
 }
+
+func TestPullCreate(t *testing.T) {
+	defer gock.Off()
+
+	gock.New("https://api.github.com").
+		Post("/repos/octocat/hello-world/pulls").
+		Reply(201).
+		Type("application/json").
+		SetHeaders(mockHeaders).
+		File("testdata/pr.json")
+
+	input := scm.PullRequestInput{
+		Title:  "new-feature",
+		Body:   "Please pull these awesome changes",
+		Source: "new-topic",
+		Target: "master",
+	}
+
+	client := NewDefault()
+	got, res, err := client.PullRequests.Create(context.Background(), "octocat/hello-world", &input)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	want := new(scm.PullRequest)
+	raw, _ := ioutil.ReadFile("testdata/pr.json.golden")
+	json.Unmarshal(raw, want)
+
+	if diff := cmp.Diff(got, want); diff != "" {
+		t.Errorf("Unexpected Results")
+		t.Log(diff)
+	}
+
+	t.Run("Request", testRequest(res))
+	t.Run("rate", testRate(res))
+}