title: How to call a lambda callback with mockk
body: <p>I create a mock of a class with mockk. 
  On this mock I now call a method that gets a lambda as a parameter. </p>
  
  <p>This lambda serves as a callback to deliver state changes of the callback to the caller of the method. </p>
  
  <pre><code>class ObjectToMock() {
      fun methodToCall(someValue: String?, observer: (State) -&gt; Unit) {
          ...
      }
  }
  </code></pre>
  
  <p>How do I configure the mock to call the passed lambda?</p>