Merge branch 'zj-mattermost-command-help-message' into 'master'

Add help section for MM commands

## What should this MR do

Check @pedroms' design for the Mattermost service screen: https://gitlab.com/gitlab-org/gitlab-ce/issues/22540

Now this has to be implemented, I've created a clean canvas for you, @lbennett, to draw on.

## Does this MR meet the acceptance criteria?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !7558

2 files changed, 48 insertions, 0 deletions

diff --git a/spec/features/projects/services/mattermost_slash_command_spec.rb b/spec/features/projects/services/mattermost_slash_command_spec.rb
new file mode 100644
index 00000000000..f474e7e891b
--- /dev/null
+++ b/spec/features/projects/services/mattermost_slash_command_spec.rb
@@ -0,0 +1,48 @@
+require 'spec_helper'
+
+feature 'Setup Mattermost slash commands', feature: true do
+  include WaitForAjax
+
+  let(:user) { create(:user) }
+  let(:project) { create(:project) }
+  let(:service) { project.create_mattermost_slash_commands_service }
+
+  before do
+    project.team << [user, :master]
+    login_as(user)
+  end
+
+  describe 'user visites the mattermost slash command config page', js: true do
+    it 'shows a help message' do
+      visit edit_namespace_project_service_path(project.namespace, project, service)
+
+      wait_for_ajax
+
+      expect(page).to have_content("This service allows GitLab users to perform common")
+    end
+  end
+
+  describe 'saving a token' do
+    let(:token) { ('a'..'z').to_a.join }
+
+    it 'shows the token after saving' do
+      visit edit_namespace_project_service_path(project.namespace, project, service)
+
+      fill_in 'service_token', with: token
+      click_on 'Save'
+
+      value = find_field('service_token').value
+
+      expect(value).to eq(token)
+    end
+  end
+
+  describe 'the trigger url' do
+    it 'shows the correct url' do
+      visit edit_namespace_project_service_path(project.namespace, project, service)
+
+      value = find_field('request_url').value
+      expect(value).to match("api/v3/projects/#{project.id}/services/mattermost_slash_commands/trigger")
+    end
+  end
+end
diff --git a/spec/features/projects/slack_service/slack_service_spec.rb b/spec/features/projects/services/slack_service_spec.rb
index 16541f51d98..16541f51d98 100644
--- a/spec/features/projects/slack_service/slack_service_spec.rb
+++ b/spec/features/projects/services/slack_service_spec.rb