1 files changed, 40 insertions, 0 deletions
diff --git a/spec/frontend/diffs/utils/preferences_spec.js b/spec/frontend/diffs/utils/preferences_spec.js
new file mode 100644
index 00000000000..a48db1d7512
--- /dev/null
+++ b/spec/frontend/diffs/utils/preferences_spec.js
@@ -0,0 +1,40 @@
+import Cookies from 'js-cookie';
+import { getParameterValues } from '~/lib/utils/url_utility';
+
+import { fileByFile } from '~/diffs/utils/preferences';
+import {
+  DIFF_FILE_BY_FILE_COOKIE_NAME,
+  DIFF_VIEW_FILE_BY_FILE,
+  DIFF_VIEW_ALL_FILES,
+} from '~/diffs/constants';
+
+jest.mock('~/lib/utils/url_utility');
+
+describe('diffs preferences', () => {
+  describe('fileByFile', () => {
+    it.each`
+      result   | preference | cookie                    | searchParam
+      ${false} | ${false}   | ${undefined}              | ${undefined}
+      ${true}  | ${true}    | ${undefined}              | ${undefined}
+      ${true}  | ${false}   | ${DIFF_VIEW_FILE_BY_FILE} | ${undefined}
+      ${false} | ${true}    | ${DIFF_VIEW_ALL_FILES}    | ${undefined}
+      ${true}  | ${false}   | ${undefined}              | ${[DIFF_VIEW_FILE_BY_FILE]}
+      ${false} | ${true}    | ${undefined}              | ${[DIFF_VIEW_ALL_FILES]}
+      ${true}  | ${false}   | ${DIFF_VIEW_FILE_BY_FILE} | ${[DIFF_VIEW_FILE_BY_FILE]}
+      ${true}  | ${true}    | ${DIFF_VIEW_ALL_FILES}    | ${[DIFF_VIEW_FILE_BY_FILE]}
+      ${false} | ${false}   | ${DIFF_VIEW_ALL_FILES}    | ${[DIFF_VIEW_ALL_FILES]}
+      ${false} | ${true}    | ${DIFF_VIEW_FILE_BY_FILE} | ${[DIFF_VIEW_ALL_FILES]}
+    `(
+      'should return $result when { preference: $preference, cookie: $cookie, search: $searchParam }',
+      ({ result, preference, cookie, searchParam }) => {
+        if (cookie) {
+          Cookies.set(DIFF_FILE_BY_FILE_COOKIE_NAME, cookie);
+        }
+
+        getParameterValues.mockReturnValue(searchParam);
+
+        expect(fileByFile(preference)).toBe(result);
+      },
+    );
+  });
+});