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diff --git a/spec/frontend/lib/utils/axios_startup_calls_spec.js b/spec/frontend/lib/utils/axios_startup_calls_spec.js
new file mode 100644
index 00000000000..e804cae7914
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+++ b/spec/frontend/lib/utils/axios_startup_calls_spec.js
@@ -0,0 +1,131 @@
+import axios from 'axios';
+import MockAdapter from 'axios-mock-adapter';
+import setupAxiosStartupCalls from '~/lib/utils/axios_startup_calls';
+
+describe('setupAxiosStartupCalls', () => {
+  const AXIOS_RESPONSE = { text: 'AXIOS_RESPONSE' };
+  const STARTUP_JS_RESPONSE = { text: 'STARTUP_JS_RESPONSE' };
+  let mock;
+
+  function mockFetchCall(status) {
+    const p = {
+      ok: status >= 200 && status < 300,
+      status,
+      headers: new Headers({ 'Content-Type': 'application/json' }),
+      statusText: `MOCK-FETCH ${status}`,
+      clone: () => p,
+      json: () => Promise.resolve(STARTUP_JS_RESPONSE),
+    };
+    return Promise.resolve(p);
+  }
+
+  function mockConsoleWarn() {
+    jest.spyOn(console, 'warn').mockImplementation();
+  }
+
+  function expectConsoleWarn(path) {
+    // eslint-disable-next-line no-console
+    expect(console.warn).toHaveBeenCalledWith(expect.stringMatching(path), expect.any(Error));
+  }
+
+  beforeEach(() => {
+    window.gl = {};
+    mock = new MockAdapter(axios);
+    mock.onGet('/non-startup').reply(200, AXIOS_RESPONSE);
+    mock.onGet('/startup').reply(200, AXIOS_RESPONSE);
+    mock.onGet('/startup-failing').reply(200, AXIOS_RESPONSE);
+  });
+
+  afterEach(() => {
+    delete window.gl;
+    axios.interceptors.request.handlers = [];
+    mock.restore();
+  });
+
+  it('if no startupCalls are registered: does not register a request interceptor', () => {
+    setupAxiosStartupCalls(axios);
+
+    expect(axios.interceptors.request.handlers.length).toBe(0);
+  });
+
+  describe('if startupCalls are registered', () => {
+    beforeEach(() => {
+      window.gl.startup_calls = {
+        '/startup': {
+          fetchCall: mockFetchCall(200),
+        },
+        '/startup-failing': {
+          fetchCall: mockFetchCall(400),
+        },
+      };
+      setupAxiosStartupCalls(axios);
+    });
+
+    it('registers a request interceptor', () => {
+      expect(axios.interceptors.request.handlers.length).toBe(1);
+    });
+
+    it('detaches the request interceptor if every startup call has been made', async () => {
+      expect(axios.interceptors.request.handlers[0]).not.toBeNull();
+
+      await axios.get('/startup');
+      mockConsoleWarn();
+      await axios.get('/startup-failing');
+
+      // Axios sets the interceptor to null
+      expect(axios.interceptors.request.handlers[0]).toBeNull();
+    });
+
+    it('delegates to startup calls if URL is registered and call is successful', async () => {
+      const { headers, data, status, statusText } = await axios.get('/startup');
+
+      expect(headers).toEqual({ 'content-type': 'application/json' });
+      expect(status).toBe(200);
+      expect(statusText).toBe('MOCK-FETCH 200');
+      expect(data).toEqual(STARTUP_JS_RESPONSE);
+      expect(data).not.toEqual(AXIOS_RESPONSE);
+    });
+
+    it('delegates to startup calls exactly once', async () => {
+      await axios.get('/startup');
+      const { data } = await axios.get('/startup');
+
+      expect(data).not.toEqual(STARTUP_JS_RESPONSE);
+      expect(data).toEqual(AXIOS_RESPONSE);
+    });
+
+    it('does not delegate to startup calls if the call is failing', async () => {
+      mockConsoleWarn();
+      const { data } = await axios.get('/startup-failing');
+
+      expect(data).not.toEqual(STARTUP_JS_RESPONSE);
+      expect(data).toEqual(AXIOS_RESPONSE);
+      expectConsoleWarn('/startup-failing');
+    });
+
+    it('does not delegate to startup call if URL is not registered', async () => {
+      const { data } = await axios.get('/non-startup');
+
+      expect(data).toEqual(AXIOS_RESPONSE);
+      expect(data).not.toEqual(STARTUP_JS_RESPONSE);
+    });
+  });
+
+  it('removes GitLab Base URL from startup call', async () => {
+    const oldGon = window.gon;
+    window.gon = { gitlab_url: 'https://example.org/gitlab' };
+
+    window.gl.startup_calls = {
+      '/startup': {
+        fetchCall: mockFetchCall(200),
+      },
+    };
+    setupAxiosStartupCalls(axios);
+
+    const { data } = await axios.get('https://example.org/gitlab/startup');
+
+    expect(data).toEqual(STARTUP_JS_RESPONSE);
+
+    window.gon = oldGon;
+  });
+});