Reorganize test cases

ts/test-node/util/getClassNamesFor_test.ts

@@ -0,0 +1,42 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+import { getClassNamesFor } from '../../util/getClassNamesFor';
+
+describe('getClassNamesFor', () => {
+  it('returns a function', () => {
+    const f = getClassNamesFor('hello-world');
+    assert.isFunction(f);
+  });
+
+  it('returns a function that adds a modifier', () => {
+    const f = getClassNamesFor('module');
+    assert.equal(f('__modifier'), 'module__modifier');
+  });
+
+  it('does not add anything if there is no modifier', () => {
+    const f = getClassNamesFor('module');
+    assert.equal(f(), '');
+    // @ts-expect-error -- test case
+    assert.equal(f(undefined && '__modifier'), '');
+  });
+
+  it('but does return the top level module if the modifier is empty string', () => {
+    const f = getClassNamesFor('module1', 'module2');
+    assert.equal(f(''), 'module1 module2');
+  });
+
+  it('adds multiple class names', () => {
+    const f = getClassNamesFor('module1', 'module2', 'module3');
+    assert.equal(
+      f('__modifier'),
+      'module1__modifier module2__modifier module3__modifier'
+    );
+  });
+
+  it('skips parent modules that are undefined', () => {
+    const f = getClassNamesFor('module1', undefined, 'module3');
+    assert.equal(f('__modifier'), 'module1__modifier module3__modifier');
+  });
+});