Merge branch '25483-broken-tabs' into 'master'

Fix TypeError: Cannot read property 'initTabs'

## What does this MR do?
Adds a default value to the `options` argument in order to prevent errors when `Pipelines` is initialised without arguments.
Adds tests to guarantee this does not happen again.

Adds back removed pipeline class to make the pipeline graph visible, `js-pipeline-graph`

## Why was this MR needed?
In the places where `Pipelines` is initialised without arguments it throws an error: `TypeError: Cannot read property 'initTabs'`


## Does this MR meet the acceptance criteria?
- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [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)

## What are the relevant issue numbers?
Closes #25483 
Closes #25493 

See merge request !8009

1 files changed, 25 insertions, 0 deletions

diff --git a/spec/javascripts/pipelines_spec.js.es6 b/spec/javascripts/pipelines_spec.js.es6
new file mode 100644
index 00000000000..85c9cf4b4f1
--- /dev/null
+++ b/spec/javascripts/pipelines_spec.js.es6
@@ -0,0 +1,25 @@
+//= require pipelines
+
+(() => {
+  describe('Pipelines', () => {
+    fixture.preload('pipeline_graph');
+
+    beforeEach(() => {
+      fixture.load('pipeline_graph');
+    });
+
+    it('should be defined', () => {
+      expect(window.gl.Pipelines).toBeDefined();
+    });
+
+    it('should create a `Pipelines` instance without options', () => {
+      expect(() => { new window.gl.Pipelines(); }).not.toThrow(); //eslint-disable-line
+    });
+
+    it('should create a `Pipelines` instance with options', () => {
+      const pipelines = new window.gl.Pipelines({ foo: 'bar' });
+
+      expect(pipelines.pipelineGraph).toBeDefined();
+    });
+  });
+})();