Consider that a GH exists only if both `ref`, and `sha` exist

lib/gitlab/github_import/branch_formatter.rb

@@ -4,7 +4,7 @@ module Gitlab
       delegate :repo, :sha, :ref, to: :raw_data
 
       def exists?
-        project.repository.branch_exists?(ref)
+        branch_exists? && commit_exists?
       end
 
       def name
@@ -15,11 +15,15 @@ module Gitlab
         repo.present?
       end
 
-      def valid?
-        repo.present?
+      private
+
+      def branch_exists?
+        project.repository.branch_exists?(ref)
       end
 
-      private
+      def commit_exists?
+        project.repository.commit(sha).present?
+      end
 
       def short_id
         sha.to_s[0..7]

spec/lib/gitlab/github_import/branch_formatter_spec.rb

@@ -2,17 +2,18 @@ require 'spec_helper'
 
 describe Gitlab::GithubImport::BranchFormatter, lib: true do
   let(:project) { create(:project) }
+  let(:commit) { create(:commit, project: project) }
   let(:repo) { double }
   let(:raw) do
     {
       ref: 'feature',
       repo: repo,
-      sha: '2e5d3239642f9161dcbbc4b70a211a68e5e45e2b'
+      sha: commit.id
     }
   end
 
   describe '#exists?' do
-    it 'returns true when branch exists' do
+    it 'returns true when both branch, and commit exists' do
       branch = described_class.new(project, double(raw))
 
       expect(branch.exists?).to eq true
@@ -23,6 +24,12 @@ describe Gitlab::GithubImport::BranchFormatter, lib: true do
 
       expect(branch.exists?).to eq false
     end
+
+    it 'returns false when commit does not exist' do
+      branch = described_class.new(project, double(raw.merge(sha: '2e5d3239642f9161dcbbc4b70a211a68e5e45e2b')))
+
+      expect(branch.exists?).to eq false
+    end
   end
 
   describe '#name' do
@@ -33,7 +40,7 @@ describe Gitlab::GithubImport::BranchFormatter, lib: true do
     end
 
     it 'returns formatted ref when branch does not exist' do
-      branch = described_class.new(project, double(raw.merge(ref: 'removed-branch')))
+      branch = described_class.new(project, double(raw.merge(ref: 'removed-branch', sha: '2e5d3239642f9161dcbbc4b70a211a68e5e45e2b')))
 
       expect(branch.name).to eq 'removed-branch-2e5d3239'
     end
@@ -51,18 +58,18 @@ describe Gitlab::GithubImport::BranchFormatter, lib: true do
     it 'returns raw sha' do
       branch = described_class.new(project, double(raw))
 
-      expect(branch.sha).to eq '2e5d3239642f9161dcbbc4b70a211a68e5e45e2b'
+      expect(branch.sha).to eq commit.id
     end
   end
 
   describe '#valid?' do
-    it 'returns true when repository exists' do
+    it 'returns true when raw repo is present' do
       branch = described_class.new(project, double(raw))
 
       expect(branch.valid?).to eq true
     end
 
-    it 'returns false when repository does not exist' do
+    it 'returns false when raw repo is blank' do
       branch = described_class.new(project, double(raw.merge(repo: nil)))
 
       expect(branch.valid?).to eq false

spec/lib/gitlab/github_import/pull_request_formatter_spec.rb

@@ -2,11 +2,13 @@ require 'spec_helper'
 
 describe Gitlab::GithubImport::PullRequestFormatter, lib: true do
   let(:project) { create(:project) }
+  let(:source_sha) { create(:commit, project: project).id }
+  let(:target_sha) { create(:commit, project: project, git_commit: RepoHelpers.another_sample_commit).id }
   let(:repository) { double(id: 1, fork: false) }
   let(:source_repo) { repository }
-  let(:source_branch) { double(ref: 'feature', repo: source_repo, sha: '2e5d3239642f9161dcbbc4b70a211a68e5e45e2b') }
+  let(:source_branch) { double(ref: 'feature', repo: source_repo, sha: source_sha) }
   let(:target_repo) { repository }
-  let(:target_branch) { double(ref: 'master', repo: target_repo, sha: '8ffb3c15a5475e59ae909384297fede4badcb4c7') }
+  let(:target_branch) { double(ref: 'master', repo: target_repo, sha: target_sha) }
   let(:octocat) { double(id: 123456, login: 'octocat') }
   let(:created_at) { DateTime.strptime('2011-01-26T19:01:12Z') }
   let(:updated_at) { DateTime.strptime('2011-01-27T19:01:12Z') }
@@ -41,10 +43,10 @@ describe Gitlab::GithubImport::PullRequestFormatter, lib: true do
           description: "*Created by: octocat*\n\nPlease pull these awesome changes",
           source_project: project,
           source_branch: 'feature',
-          head_source_sha: '2e5d3239642f9161dcbbc4b70a211a68e5e45e2b',
+          head_source_sha: source_sha,
           target_project: project,
           target_branch: 'master',
-          base_target_sha: '8ffb3c15a5475e59ae909384297fede4badcb4c7',
+          base_target_sha: target_sha,
           state: 'opened',
           milestone: nil,
           author_id: project.creator_id,
@@ -68,10 +70,10 @@ describe Gitlab::GithubImport::PullRequestFormatter, lib: true do
           description: "*Created by: octocat*\n\nPlease pull these awesome changes",
           source_project: project,
           source_branch: 'feature',
-          head_source_sha: '2e5d3239642f9161dcbbc4b70a211a68e5e45e2b',
+          head_source_sha: source_sha,
           target_project: project,
           target_branch: 'master',
-          base_target_sha: '8ffb3c15a5475e59ae909384297fede4badcb4c7',
+          base_target_sha: target_sha,
           state: 'closed',
           milestone: nil,
           author_id: project.creator_id,
@@ -95,10 +97,10 @@ describe Gitlab::GithubImport::PullRequestFormatter, lib: true do
           description: "*Created by: octocat*\n\nPlease pull these awesome changes",
           source_project: project,
           source_branch: 'feature',
-          head_source_sha: '2e5d3239642f9161dcbbc4b70a211a68e5e45e2b',
+          head_source_sha: source_sha,
           target_project: project,
           target_branch: 'master',
-          base_target_sha: '8ffb3c15a5475e59ae909384297fede4badcb4c7',
+          base_target_sha: target_sha,
           state: 'merged',
           milestone: nil,
           author_id: project.creator_id,