Adds tests to prevent future errors.

Fix undefined variable in es5

app/assets/javascripts/pipelines.js.es6

@@ -16,7 +16,7 @@
     addMarginToBuildColumns() {
       this.pipelineGraph = document.querySelector('.pipeline-graph');
       const secondChildBuildNodes = document.querySelector('.pipeline-graph').querySelectorAll('.build:nth-child(2)');
-      for (buildNodeIndex in secondChildBuildNodes) {
+      for (const buildNodeIndex in secondChildBuildNodes) {
         const buildNode = secondChildBuildNodes[buildNodeIndex];
         const firstChildBuildNode = buildNode.previousElementSibling;
         if (!firstChildBuildNode || !firstChildBuildNode.matches('.build')) continue;

changelogs/unreleased/25483-broken-tabs.yml

 ---
 title: Fix TypeError: Cannot read property 'initTabs' on commit builds tab
-merge_request:
+merge_request: 8009
 author:

spec/javascripts/fixtures/pipeline_graph.html.haml

+%div.pipeline-visualization.pipeline-graph
+  %ul.stage-column-list
+    %li.stage-column
+      .stage-name
+        %a{:href => "/"}
+          Test
+          .builds-container
+            %ul
+              %li.build
+                .curve
+                .build-content
+                  %a
+                    %svg
+                    .ci-status-text
+                      stop_review

spec/javascripts/pipelines_spec.js.es6

+//= 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();
+    });
+  });
+})();