Adds ability to update pull request branch

lib/octokit/client/pull_requests.rb

@@ -276,6 +276,17 @@ def pull_request_files(repo, number, options = {})
       end
       alias pull_files pull_request_files
 
+      # Update a pull request branch
+      #
+      # @see https://developer.github.com/v3/pulls/#update-a-pull-request-branch
+      # @param repo [Integer, String, Hash, Repository] A GitHub repository
+      # @param number [Integer] Number of pull request
+      # @param options [Hash] Optional parameters (e.g. expected_head_sha)
+      # @return [Boolean] True if the pull request branch has been updated
+      def update_pull_request_branch(repo, number, options = {})
+        boolean_from_response(:put, "#{Repository.path repo}/pulls/#{number}/update-branch", options)
+      end
+
       # Merge a pull request
       #
       # @see https://developer.github.com/v3/pulls/#merge-a-pull-request-merge-button

spec/octokit/client/pull_requests_spec.rb

@@ -136,6 +136,40 @@
     end
   end # new @pull methods
 
+  # stub this so we don't have to set up new fixture data
+  describe '.update_pull_request_branch' do
+    let(:repo) { 'api-playground/api-sandbox' }
+    let(:pull_number) { 321 }
+    let(:update_branch_url) { github_url("/repos/#{repo}/pulls/#{pull_number}/update-branch") }
+    let(:status) { 202 }
+
+    before(:each) do
+      stub_put(update_branch_url).to_return(status: status)
+    end
+
+    it 'updates the pull request branch' do
+      result = @client.update_pull_request_branch(repo, pull_number)
+      assert_requested :put, update_branch_url
+      expect(result).to eq(true)
+    end
+
+    context 'when the request fails with a 403 Forbidden' do
+      let(:status) { 403 }
+
+      it 'raises an exception' do
+        expect { @client.update_pull_request_branch(repo, pull_number) }.to raise_error(Octokit::Forbidden)
+      end
+    end
+
+    context 'when the request fails with a 422 Unprocessable Entity' do
+      let(:status) { 422 }
+
+      it 'raises an exception' do
+        expect { @client.update_pull_request_branch(repo, pull_number) }.to raise_error(Octokit::UnprocessableEntity)
+      end
+    end
+  end # .update_pull_request_branch
+
   # stub this so we don't have to set up new fixture data
   describe '.merge_pull_request' do
     it 'merges the pull request' do