title: what is the purpose of toBeFalsy()?
body: <p>I have an input in angular inside a template driven form.</p>
  <pre class="lang-html prettyprint-override"><code>&lt;form  name=&quot;editForm&quot; role=&quot;form&quot; novalidate (ngSubmit)=&quot;save()&quot; #editForm=&quot;ngForm&quot;&gt;
  
  &lt;input #cardInput type=&quot;text&quot; class=&quot;form-control&quot; name=&quot;tarjetaSanitaria&quot; id=&quot;field_tarjetaSanitaria&quot;
                      [(ngModel)]=&quot;paciente.tarjetaSanitaria&quot; maxlength=&quot;20&quot;/&gt;
                 &lt;small class=&quot;form-text text-danger&quot;
                     [hidden]=&quot;!editForm.controls.tarjetaSanitaria?.errors?.maxlength&quot; jhiTranslate=&quot;entity.validation.maxlength&quot; translateValues=&quot;{ max: 20 }&quot;&gt;
                     This field cannot be longer than 20 characters.
                  &lt;/small&gt;
  </code></pre>
  <p>How can I unit test that it can only input texts that have a maxlength  of 20.</p>
  <p>I have this in my component:</p>
  <pre class="lang-js prettyprint-override"><code>export class PacienteDialogComponent implements OnInit {
    paciente: Paciente;
        constructor( //other things not paciente
        ){
      }
  .....
  </code></pre>
  <p>And this is my paciente.model.ts that has the property of the input tarjetaSanitaria I wanna test:</p>
  <pre class="lang-js prettyprint-override"><code>import { BaseEntity } from './../../shared';
  
  export class Paciente implements BaseEntity {
      constructor( public tarjetaSanitaria?: string)
      
      {
      }
  }
  </code></pre>
  <p>And here is my testing class:</p>
  <pre class="lang-js prettyprint-override"><code>  import { Paciente } from...
  import { PacienteDialogComponent } from '..
   describe(....){
  
   let comp: PacienteDialogComponent;
          let fixture: ComponentFixture&lt;PacienteDialogComponent&gt;;....
  
    beforeEach(() =&gt; {
              fixture = TestBed.createComponent(PacienteDialogComponent);
              comp = fixture.componentInstance;...
  
        it ('Input validation', async(() =&gt; {
                     
                       comp.cardInput.nativeElement.value = 'dddddddddddddddddddddddddddddddddddddddddddddddddddddd' ; // a text longer than 20 characters
                      expect(comp.cardInput.nativeElement.valid).toBeFalsy();
                    }));
  </code></pre>
  <p>The test passes, but anyway is this the right way to test the validation of an input?  What happens after toBeFalsy()? How can the user know that this is false? Can I output a message in this case if it is false,?</p>
  <p>Is therea nother way to test the form inputs validation?</p>