title: How to disable Flow (JS) type checking for a single line
body: <p>Some of my unit tests involve passing invalid (improperly typed) data to a function. For example:</p>
  
  <pre><code>// user.js
  
  type User = {
      id: number,
      name: string,
      email: string
  }
  
  export function validateUser(user: User): Promise&lt;void&gt; {
      return new Promise((resolve, reject) =&gt; {
          // resolve if user is valid, reject if not
      })
  }
  </code></pre>
  
  <pre><code>// user.unit.js
  
  import {validateUser} from '../user.js' 
  
  describe('validateUser', () =&gt; {
      it('should reject if user is not valid', () =&gt; {
          const invalidUser: User = {}
          expect(validateUser(invalidUser)).to.be.rejected
      })
  })
  </code></pre>
  
  <p>Since the <code>invalidUser</code> variable does not conform to the <code>User</code> type, I get a flow error:</p>
  
  <pre><code>Cannot call validateUser with invalidUser bound to user because:
   • property id is missing in object literal [1] but exists in User [2].
   • property name is missing in object literal [1] but exists in User [2].
   • property email is missing in object literal [1] but exists in User [2].
  </code></pre>
  
  <p>Obviously I want this variable to be invalid, so how can I disable flow type checking for this single instance?</p>