hunk.code_window:         }
         }
       };
       const service = interpret(Machine(invalidMachine));
       assert.throws(
         () => service.start(),
         `Initial state 'create' not found on 'fetchMachine'`
       );
     });
     it('should not update when stopped', () => {
       let state = lightMachine.initialState;
  
hunk.labels: keep keep keep keep replace replace replace replace replace keep keep keep keep
hunk.after_edit:     assert.throws(() => {
         interpret(Machine(invalidMachine)).start();
       }, `Initial state 'create' not found on 'fetchMachine'`);
  
hunk.file_path: test/interpreter.test.ts
hunk.type: replace
file: # Concepts
  
  XState is a library for creating, interpreting, and executing statecharts. Statecharts are a formalism for modeling stateful, reactive systems. Computer scientist David Harel presented this formalism as an extension to state machines in his 1987 paper [Statecharts: A Visual Formalism for Complex Systems](http://www.inf.ed.ac.uk/teaching/courses/seoc/2005_2006/resources/statecharts.pdf).
  
  ## More Resources
  
  - [The World of Statecharts](https://statecharts.github.io/) by Erik Mogensen
  - [Finite-state machine](https://en.wikipedia.org/wiki/Finite-state_machine) article on Wikipedia
  