protractor.js

  var ps = element.all(by.css('p'));

  it('should let you toggle the class', function() {

    expect(ps.first().getAttribute('class')).not.toMatch(/bold/);
    expect(ps.first().getAttribute('class')).not.toMatch(/red/);

    element(by.model('important')).click();
    expect(ps.first().getAttribute('class')).toMatch(/bold/);

    element(by.model('error')).click();
    expect(ps.first().getAttribute('class')).toMatch(/red/);
  });

  it('should let you toggle string example', function() {
    expect(ps.get(1).getAttribute('class')).toBe('');
    element(by.model('style')).clear();
    element(by.model('style')).sendKeys('red');
    expect(ps.get(1).getAttribute('class')).toBe('red');
  });

  it('array example should have 3 classes', function() {
    expect(ps.last().getAttribute('class')).toBe('');
    element(by.model('style1')).sendKeys('bold');
    element(by.model('style2')).sendKeys('strike');
    element(by.model('style3')).sendKeys('red');
    expect(ps.last().getAttribute('class')).toBe('bold strike red');
  });