refactor merge request build service

add changelog entry

replace local variables `merge_request` with instance ones

modify `MergeRequests::BuildService` to fix failed tests

extract `assign_target_project` method

remove unnecessary instance variables

remove exclamation marks and rewrite conditionals to improve readability

extract `params_does_not_contain_branches?` method, rename `unprepared_merge_request` method to `uncreatable_merge_request`

replace instance variables `merge_request` and `error_messages` with getters and setters; divide `set_title_and_description` method on two separate ones

refactor `execute` method

return `set_title_and_description` method

rename `branches_selected?` method to `branches_present?` to make it more different from `branches_specified?`

fixes after discussion

renamed method branches_valid?

fix space

return assigning methods into `execute` method

simplify `find_target_branch` and `find_source_project` methods

fix spec `merge request issuable record that supports slash commands in its description and notes`

1 files changed, 1 insertions, 1 deletions

diff --git a/spec/features/merge_requests/user_uses_slash_commands_spec.rb b/spec/features/merge_requests/user_uses_slash_commands_spec.rb
index b13674b4db9..2582a540240 100644
--- a/spec/features/merge_requests/user_uses_slash_commands_spec.rb
+++ b/spec/features/merge_requests/user_uses_slash_commands_spec.rb
@@ -11,7 +11,7 @@ feature 'Merge Requests > User uses slash commands', feature: true, js: true do
 
   it_behaves_like 'issuable record that supports slash commands in its description and notes', :merge_request do
     let(:issuable) { create(:merge_request, source_project: project) }
-    let(:new_url_opts) { { merge_request: { source_branch: 'feature' } } }
+    let(:new_url_opts) { { merge_request: { source_branch: 'feature', target_branch: 'master' } } }
   end
 
   describe 'merge-request-only commands' do