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diff --git a/spec/frontend/vue_shared/components/source_viewer/source_viewer_deprecated_spec.js b/spec/frontend/vue_shared/components/source_viewer/source_viewer_deprecated_spec.js
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+import hljs from 'highlight.js/lib/core';
+import Vue from 'vue';
+import VueRouter from 'vue-router';
+import { shallowMountExtended } from 'helpers/vue_test_utils_helper';
+import SourceViewer from '~/vue_shared/components/source_viewer/source_viewer_deprecated.vue';
+import { registerPlugins } from '~/vue_shared/components/source_viewer/plugins/index';
+import Chunk from '~/vue_shared/components/source_viewer/components/chunk_deprecated.vue';
+import {
+  EVENT_ACTION,
+  EVENT_LABEL_VIEWER,
+  EVENT_LABEL_FALLBACK,
+  ROUGE_TO_HLJS_LANGUAGE_MAP,
+  LINES_PER_CHUNK,
+} from '~/vue_shared/components/source_viewer/constants';
+import waitForPromises from 'helpers/wait_for_promises';
+import LineHighlighter from '~/blob/line_highlighter';
+import eventHub from '~/notes/event_hub';
+import Tracking from '~/tracking';
+
+jest.mock('~/blob/line_highlighter');
+jest.mock('highlight.js/lib/core');
+jest.mock('~/vue_shared/components/source_viewer/plugins/index');
+Vue.use(VueRouter);
+const router = new VueRouter();
+
+const generateContent = (content, totalLines = 1, delimiter = '\n') => {
+  let generatedContent = '';
+  for (let i = 0; i < totalLines; i += 1) {
+    generatedContent += `Line: ${i + 1} = ${content}${delimiter}`;
+  }
+  return generatedContent;
+};
+
+const execImmediately = (callback) => callback();
+
+describe('Source Viewer component', () => {
+  let wrapper;
+  const language = 'docker';
+  const mappedLanguage = ROUGE_TO_HLJS_LANGUAGE_MAP[language];
+  const chunk1 = generateContent('// Some source code 1', 70);
+  const chunk2 = generateContent('// Some source code 2', 70);
+  const chunk3 = generateContent('// Some source code 3', 70, '\r\n');
+  const chunk3Result = generateContent('// Some source code 3', 70, '\n');
+  const content = chunk1 + chunk2 + chunk3;
+  const path = 'some/path.js';
+  const blamePath = 'some/blame/path.js';
+  const fileType = 'javascript';
+  const DEFAULT_BLOB_DATA = { language, rawTextBlob: content, path, blamePath, fileType };
+  const highlightedContent = `<span data-testid='test-highlighted' id='LC1'>${content}</span><span id='LC2'></span>`;
+
+  const createComponent = async (blob = {}) => {
+    wrapper = shallowMountExtended(SourceViewer, {
+      router,
+      propsData: { blob: { ...DEFAULT_BLOB_DATA, ...blob } },
+    });
+    await waitForPromises();
+  };
+
+  const findChunks = () => wrapper.findAllComponents(Chunk);
+
+  beforeEach(() => {
+    hljs.highlight.mockImplementation(() => ({ value: highlightedContent }));
+    hljs.highlightAuto.mockImplementation(() => ({ value: highlightedContent }));
+    jest.spyOn(window, 'requestIdleCallback').mockImplementation(execImmediately);
+    jest.spyOn(eventHub, '$emit');
+    jest.spyOn(Tracking, 'event');
+
+    return createComponent();
+  });
+
+  afterEach(() => wrapper.destroy());
+
+  describe('event tracking', () => {
+    it('fires a tracking event when the component is created', () => {
+      const eventData = { label: EVENT_LABEL_VIEWER, property: language };
+      expect(Tracking.event).toHaveBeenCalledWith(undefined, EVENT_ACTION, eventData);
+    });
+
+    it('does not emit an error event when the language is supported', () => {
+      expect(wrapper.emitted('error')).toBeUndefined();
+    });
+
+    it('fires a tracking event and emits an error when the language is not supported', () => {
+      const unsupportedLanguage = 'apex';
+      const eventData = { label: EVENT_LABEL_FALLBACK, property: unsupportedLanguage };
+      createComponent({ language: unsupportedLanguage });
+
+      expect(Tracking.event).toHaveBeenCalledWith(undefined, EVENT_ACTION, eventData);
+      expect(wrapper.emitted('error')).toHaveLength(1);
+    });
+  });
+
+  describe('legacy fallbacks', () => {
+    it('tracks a fallback event and emits an error when viewing python files', () => {
+      const fallbackLanguage = 'python';
+      const eventData = { label: EVENT_LABEL_FALLBACK, property: fallbackLanguage };
+      createComponent({ language: fallbackLanguage });
+
+      expect(Tracking.event).toHaveBeenCalledWith(undefined, EVENT_ACTION, eventData);
+      expect(wrapper.emitted('error')).toHaveLength(1);
+    });
+  });
+
+  describe('highlight.js', () => {
+    beforeEach(() => createComponent({ language: mappedLanguage }));
+
+    it('registers our plugins for Highlight.js', () => {
+      expect(registerPlugins).toHaveBeenCalledWith(hljs, fileType, content);
+    });
+
+    it('registers the language definition', async () => {
+      const languageDefinition = await import(`highlight.js/lib/languages/${mappedLanguage}`);
+
+      expect(hljs.registerLanguage).toHaveBeenCalledWith(
+        mappedLanguage,
+        languageDefinition.default,
+      );
+    });
+
+    it('registers json language definition if fileType is package_json', async () => {
+      await createComponent({ language: 'json', fileType: 'package_json' });
+      const languageDefinition = await import(`highlight.js/lib/languages/json`);
+
+      expect(hljs.registerLanguage).toHaveBeenCalledWith('json', languageDefinition.default);
+    });
+
+    it('correctly maps languages starting with uppercase', async () => {
+      await createComponent({ language: 'Ruby' });
+      const languageDefinition = await import(`highlight.js/lib/languages/ruby`);
+
+      expect(hljs.registerLanguage).toHaveBeenCalledWith('ruby', languageDefinition.default);
+    });
+
+    it('highlights the first chunk', () => {
+      expect(hljs.highlight).toHaveBeenCalledWith(chunk1.trim(), { language: mappedLanguage });
+      expect(findChunks().at(0).props('isFirstChunk')).toBe(true);
+    });
+
+    describe('auto-detects if a language cannot be loaded', () => {
+      beforeEach(() => createComponent({ language: 'some_unknown_language' }));
+
+      it('highlights the content with auto-detection', () => {
+        expect(hljs.highlightAuto).toHaveBeenCalledWith(chunk1.trim());
+      });
+    });
+  });
+
+  describe('rendering', () => {
+    it.each`
+      chunkIndex | chunkContent    | totalChunks
+      ${0}       | ${chunk1}       | ${0}
+      ${1}       | ${chunk2}       | ${3}
+      ${2}       | ${chunk3Result} | ${3}
+    `('renders chunk $chunkIndex', ({ chunkIndex, chunkContent, totalChunks }) => {
+      const chunk = findChunks().at(chunkIndex);
+
+      expect(chunk.props('content')).toContain(chunkContent.trim());
+
+      expect(chunk.props()).toMatchObject({
+        totalLines: LINES_PER_CHUNK,
+        startingFrom: LINES_PER_CHUNK * chunkIndex,
+        totalChunks,
+      });
+    });
+
+    it('emits showBlobInteractionZones on the eventHub when chunk appears', () => {
+      findChunks().at(0).vm.$emit('appear');
+      expect(eventHub.$emit).toHaveBeenCalledWith('showBlobInteractionZones', path);
+    });
+  });
+
+  describe('LineHighlighter', () => {
+    it('instantiates the lineHighlighter class', async () => {
+      expect(LineHighlighter).toHaveBeenCalledWith({ scrollBehavior: 'auto' });
+    });
+  });
+});