Make spec insusceptible to test branch list changes

After adding a new branch to TestEnv::BRANCH_SHA spec
Projects::BranchesByModeService started failing.
It required adjusting every time branches list was changed.
Since adjusting that array also requires one to manually remove
directories ./tmp/tests/gitlab-test*, it have initially gone unnoticed.
This change makes the spec calculate the expected values dynamically,
so future changes in branch list shouldn't break this spec.

spec/services/projects/branches_by_mode_service_spec.rb

@@ -13,20 +13,22 @@ RSpec.describe Projects::BranchesByModeService do
 
   describe '#execute' do
     context 'page is passed' do
-      let(:params) { { page: 4, mode: 'all', offset: 3 } }
+      let(:page) { (TestEnv::BRANCH_SHA.length.to_f / Kaminari.config.default_per_page).ceil }
+      let(:params) { { page: page, mode: 'all', offset: page - 1 } }
 
       it 'uses offset pagination' do
         expect(finder).to receive(:fetch_branches_via_offset_pagination).and_call_original
 
         branches, prev_page, next_page = subject
+        remaining = TestEnv::BRANCH_SHA.length % Kaminari.config.default_per_page
 
-        expect(branches.size).to eq(11)
+        expect(branches.size).to eq(remaining > 0 ? remaining : 20)
         expect(next_page).to be_nil
-        expect(prev_page).to eq("/#{project.full_path}/-/branches/all?offset=2&page=3")
+        expect(prev_page).to eq("/#{project.full_path}/-/branches/all?offset=#{page - 2}&page=#{page - 1}")
       end
 
       context 'but the page does not contain any branches' do
-        let(:params) { { page: 10, mode: 'all' } }
+        let(:params) { { page: 100, mode: 'all' } }
 
         it 'uses offset pagination' do
           expect(finder).to receive(:fetch_branches_via_offset_pagination).and_call_original
@@ -61,9 +63,10 @@ RSpec.describe Projects::BranchesByModeService do
         expect(finder).to receive(:fetch_branches_via_offset_pagination).and_call_original
 
         branches, prev_page, next_page = subject
+        expected_page_token = ERB::Util.url_encode(TestEnv::BRANCH_SHA.sort[19][0])
 
         expect(branches.size).to eq(20)
-        expect(next_page).to eq("/#{project.full_path}/-/branches/all?offset=1&page_token=conflict-resolvable")
+        expect(next_page).to eq("/#{project.full_path}/-/branches/all?offset=1&page_token=#{expected_page_token}")
         expect(prev_page).to be_nil
       end
     end
@@ -75,26 +78,31 @@ RSpec.describe Projects::BranchesByModeService do
 
       it 'returns branches for the first page' do
         branches, prev_page, next_page = subject
+        expected_page_token = ERB::Util.url_encode(TestEnv::BRANCH_SHA.sort[19][0])
 
         expect(branches.size).to eq(20)
-        expect(next_page).to eq("/#{project.full_path}/-/branches/all?offset=1&page_token=conflict-resolvable")
+        expect(next_page).to eq("/#{project.full_path}/-/branches/all?offset=1&page_token=#{expected_page_token}")
         expect(prev_page).to be_nil
       end
 
       context 'when second page is requested' do
-        let(:params) { { page_token: 'conflict-resolvable', mode: 'all', sort: 'name_asc', offset: 1 } }
+        let(:page_token) { 'conflict-resolvable' }
+        let(:params) { { page_token: page_token, mode: 'all', sort: 'name_asc', offset: 1 } }
 
         it 'returns branches for the first page' do
           branches, prev_page, next_page = subject
+          branch_index = TestEnv::BRANCH_SHA.sort.find_index { |a| a[0] == page_token }
+          expected_page_token = ERB::Util.url_encode(TestEnv::BRANCH_SHA.sort[20 + branch_index][0])
 
           expect(branches.size).to eq(20)
-          expect(next_page).to eq("/#{project.full_path}/-/branches/all?offset=2&page_token=improve%2Fawesome&sort=name_asc")
+          expect(next_page).to eq("/#{project.full_path}/-/branches/all?offset=2&page_token=#{expected_page_token}&sort=name_asc")
           expect(prev_page).to eq("/#{project.full_path}/-/branches/all?offset=0&page=1&sort=name_asc")
         end
       end
 
       context 'when last page is requested' do
-        let(:params) { { page_token: 'signed-commits', mode: 'all', sort: 'name_asc', offset: 4 } }
+        let(:page_token) { TestEnv::BRANCH_SHA.sort[-16][0] }
+        let(:params) { { page_token: page_token, mode: 'all', sort: 'name_asc', offset: 4 } }
 
         it 'returns branches after the specified branch' do
           branches, prev_page, next_page = subject