Add doesNotHaveClass/hasNoClass() assertion

API.md

@@ -97,6 +97,8 @@ assert.dom('input[type="password"]').isNotFocused();
 
 ### hasClass
 
+-   **See: [#doesNotHaveClass](#doesnothaveclass)**
+
 Assert that the [HTMLElement][] has the `expected` CSS class using
 [`classList`](https://developer.mozilla.org/en-US/docs/Web/API/Element/classList).
 
@@ -111,6 +113,26 @@ Assert that the [HTMLElement][] has the `expected` CSS class using
 assert.dom('input[type="password"]').hasClass('secret-password-input');
 ```
 
+### doesNotHaveClass
+
+-   **See: [#hasClass](#hasclass)**
+
+Assert that the [HTMLElement][] does not have the `expected` CSS class using
+[`classList`](https://developer.mozilla.org/en-US/docs/Web/API/Element/classList).
+
+**Aliases:** `hasNoClass`
+
+**Parameters**
+
+-   `expected` **[string](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String)** 
+-   `message` **[string](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String)?** 
+
+**Examples**
+
+```javascript
+assert.dom('input[type="password"]').doesNotHaveClass('username-input');
+```
+
 ### hasText
 
 -   **See: [#hasTextContaining](#hastextcontaining)**

lib/__tests__/does-not-have-class.js

@@ -0,0 +1,64 @@
+/* eslint-env jest */
+
+import TestAssertions from "../helpers/test-assertions";
+
+describe('assert.dom(...).doesNotHaveClass()', () => {
+  let assert;
+
+  beforeEach(() => {
+    assert = new TestAssertions();
+
+    document.body.innerHTML = '<input type="password" class="secret-password-input foo">';
+  });
+
+  test('succeeds for correct content', () => {
+    assert.dom('input[type="password"]').doesNotHaveClass('username-input');
+    assert.dom(document.querySelector('input[type="password"]')).doesNotHaveClass('username-input');
+
+    expect(assert.results).toEqual([{
+      actual: 'secret-password-input foo',
+      expected: 'not: username-input',
+      message: 'Element input[type="password"] does not have CSS class "username-input"',
+      result: true,
+    }, {
+      actual: 'secret-password-input foo',
+      expected: 'not: username-input',
+      message: 'Element input.secret-password-input.foo[type="password"] does not have CSS class "username-input"',
+      result: true,
+    }]);
+  });
+
+  test('fails for wrong content', () => {
+    assert.dom('input[type="password"]').doesNotHaveClass('secret-password-input');
+    assert.dom(document.querySelector('input[type="password"]')).doesNotHaveClass('secret-password-input');
+
+    expect(assert.results).toEqual([{
+      actual: 'secret-password-input foo',
+      expected: 'not: secret-password-input',
+      message: 'Element input[type="password"] does not have CSS class "secret-password-input"',
+      result: false,
+    }, {
+      actual: 'secret-password-input foo',
+      expected: 'not: secret-password-input',
+      message: 'Element input.secret-password-input.foo[type="password"] does not have CSS class "secret-password-input"',
+      result: false,
+    }]);
+  });
+
+  test('fails for missing element', () => {
+    assert.dom('#missing').doesNotHaveClass('foo');
+
+    expect(assert.results).toEqual([{
+      message: 'Element #missing exists',
+      result: false,
+    }]);
+  });
+
+  test('throws for unexpected parameter types', () => {
+    expect(() => assert.dom(5).doesNotHaveClass('foo')).toThrow('Unexpected Parameter: 5');
+    expect(() => assert.dom(true).doesNotHaveClass('foo')).toThrow('Unexpected Parameter: true');
+    expect(() => assert.dom(undefined).doesNotHaveClass('foo')).toThrow('Unexpected Parameter: undefined');
+    expect(() => assert.dom({}).doesNotHaveClass('foo')).toThrow('Unexpected Parameter: [object Object]');
+    expect(() => assert.dom(document).doesNotHaveClass('foo')).toThrow('Unexpected Parameter: [object HTMLDocument]');
+  });
+});

lib/assertions.js

@@ -72,7 +72,6 @@ export default class DOMAssertions {
     notFocused.call(this, message);
   }
 
-
   /**
    * Assert that the [HTMLElement][] has the `expected` CSS class using
    * [`classList`](https://developer.mozilla.org/en-US/docs/Web/API/Element/classList).
@@ -82,6 +81,8 @@ export default class DOMAssertions {
    *
    * @example
    * assert.dom('input[type="password"]').hasClass('secret-password-input');
+   *
+   * @see {@link #doesNotHaveClass}
    */
   hasClass(expected, message) {
     let element = this.findTargetElement();
@@ -97,6 +98,38 @@ export default class DOMAssertions {
     this.pushResult({ result, actual, expected, message });
   }
 
+  /**
+   * Assert that the [HTMLElement][] does not have the `expected` CSS class using
+   * [`classList`](https://developer.mozilla.org/en-US/docs/Web/API/Element/classList).
+   *
+   * **Aliases:** `hasNoClass`
+   *
+   * @param {string} expected
+   * @param {string?} message
+   *
+   * @example
+   * assert.dom('input[type="password"]').doesNotHaveClass('username-input');
+   *
+   * @see {@link #hasClass}
+   */
+  doesNotHaveClass(expected, message) {
+    let element = this.findTargetElement();
+    if (!element) return;
+
+    let result = !element.classList.contains(expected);
+    let actual = element.classList.toString();
+
+    if (!message) {
+      message = `Element ${this.targetDescription} does not have CSS class "${expected}"`;
+    }
+
+    this.pushResult({ result, actual, expected: `not: ${expected}`, message });
+  }
+
+  hasNoClass(expected, message) {
+    this.doesNotHaveClass(expected, message);
+  }
+
   /**
    * Assert that the text of the [HTMLElement][] or an [HTMLElement][]
    * matching the `selector` matches the `expected` text, using the