Add AppsService.{Add,Remove}Repository methods. (google#749)

GitHub API docs:

-	https://developer.github.com/v3/apps/installations/#add-repository-to-installation
-	https://developer.github.com/v3/apps/installations/#remove-repository-from-installation

AUTHORS

@@ -77,6 +77,7 @@ i2bskn <[email protected]>
 Isao Jonas <[email protected]>
 isqua <[email protected]>
 Jameel Haffejee <[email protected]>
+Jeremy Morris <[email protected]>
 Jan Kosecki <[email protected]>
 Jihoon Chung <[email protected]>
 Jimmi Dyson <[email protected]>

github/apps_installation.go

@@ -5,7 +5,10 @@
 
 package github
 
-import "context"
+import (
+	"context"
+	"fmt"
+)
 
 // Installation represents a GitHub Apps installation.
 type Installation struct {
@@ -47,3 +50,35 @@ func (s *AppsService) ListRepos(ctx context.Context, opt *ListOptions) ([]*Repos
 
 	return r.Repositories, resp, nil
 }
+
+// AddRepository adds a single repository to an installation.
+//
+// GitHub API docs: https://developer.github.com/v3/apps/installations/#add-repository-to-installation
+func (s *AppsService) AddRepository(ctx context.Context, instID, repoID int) (*Repository, *Response, error) {
+	u := fmt.Sprintf("apps/installations/%v/repositories/%v", instID, repoID)
+	req, err := s.client.NewRequest("PUT", u, nil)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	r := new(Repository)
+	resp, err := s.client.Do(ctx, req, r)
+	if err != nil {
+		return nil, resp, err
+	}
+
+	return r, resp, nil
+}
+
+// RemoveRepository removes a single repository from an installation.
+//
+// GitHub docs: https://developer.github.com/v3/apps/installations/#remove-repository-from-installation
+func (s *AppsService) RemoveRepository(ctx context.Context, instID, repoID int) (*Response, error) {
+	u := fmt.Sprintf("apps/installations/%v/repositories/%v", instID, repoID)
+	req, err := s.client.NewRequest("DELETE", u, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	return s.client.Do(ctx, req, nil)
+}

github/apps_installation_test.go

@@ -38,3 +38,38 @@ func TestAppsService_ListRepos(t *testing.T) {
 		t.Errorf("Apps.ListRepos returned %+v, want %+v", repositories, want)
 	}
 }
+
+func TestAppsService_AddRepository(t *testing.T) {
+	setup()
+	defer teardown()
+
+	mux.HandleFunc("/apps/installations/1/repositories/1", func(w http.ResponseWriter, r *http.Request) {
+		testMethod(t, r, "PUT")
+		fmt.Fprint(w, `{"id":1,"name":"n","description":"d","owner":{"login":"l"},"license":{"key":"mit"}}`)
+	})
+
+	repo, _, err := client.Apps.AddRepository(context.Background(), 1, 1)
+	if err != nil {
+		t.Errorf("Apps.AddRepository returned error: %v", err)
+	}
+
+	want := &Repository{ID: Int(1), Name: String("n"), Description: String("d"), Owner: &User{Login: String("l")}, License: &License{Key: String("mit")}}
+	if !reflect.DeepEqual(repo, want) {
+		t.Errorf("AddRepository returned %+v, want %+v", repo, want)
+	}
+}
+
+func TestAppsService_RemoveRepository(t *testing.T) {
+	setup()
+	defer teardown()
+
+	mux.HandleFunc("/apps/installations/1/repositories/1", func(w http.ResponseWriter, r *http.Request) {
+		testMethod(t, r, "DELETE")
+		w.WriteHeader(http.StatusNoContent)
+	})
+
+	_, err := client.Apps.RemoveRepository(context.Background(), 1, 1)
+	if err != nil {
+		t.Errorf("Apps.RemoveRepository returned error: %v", err)
+	}
+}