Spellcheck: Fallback to all xx-YY locales when xx isn't available

test/app/spell_check_test.js

@@ -0,0 +1,40 @@
+const { assert } = require('chai');
+
+const { getLanguages } = require('../../app/spell_check');
+
+describe('SpellCheck', () => {
+  describe('getLanguages', () => {
+    it('works with locale and base available', () => {
+      assert.deepEqual(getLanguages('en-US', ['en-US', 'en-CA', 'en']), [
+        'en-US',
+        'en',
+      ]);
+    });
+
+    it('works with neither locale nor base available', () => {
+      assert.deepEqual(getLanguages('en-US', ['en-NZ', 'en-CA']), [
+        'en-NZ',
+        'en-CA',
+      ]);
+    });
+
+    it('works with only base locale available', () => {
+      assert.deepEqual(getLanguages('en-US', ['en', 'en-CA']), ['en']);
+    });
+
+    it('works with only full locale available', () => {
+      assert.deepEqual(getLanguages('en-US', ['en-CA', 'en-US']), ['en-US']);
+    });
+
+    it('works with base provided and base available', () => {
+      assert.deepEqual(getLanguages('en', ['en-CA', 'en-US', 'en']), ['en']);
+    });
+
+    it('works with base provided and base not available', () => {
+      assert.deepEqual(getLanguages('en', ['en-CA', 'en-US']), [
+        'en-CA',
+        'en-US',
+      ]);
+    });
+  });
+});