Log error instead of throwing. Move test to service.

src/common/services/OptionsService.test.ts

@@ -0,0 +1,22 @@
+/**
+ * Copyright (c) 2020 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { assert } from 'chai';
+import { OptionsService, DEFAULT_OPTIONS } from 'common/services/OptionsService';
+
+describe('OptionsService', () => {
+  describe('constructor', () => {
+    const originalError = console.error;
+    beforeEach(() => {
+      console.error = () => {};
+    });
+    afterEach(() => {
+      console.error = originalError;
+    });
+    it('uses default value if invalid constructor option value passed', () => {
+      assert.equal(new OptionsService({tabStopWidth: 0}).getOption('tabStopWidth'), DEFAULT_OPTIONS.tabStopWidth);
+    });
+  });
+});