Observable calls

The main purpose of this library is to provide a mean to observe function calls during unit tests. If it fits any need beyond testing, feel free to report this new usage context to enhance the documentation.

Type npm install observable-calls to get the library, you can then use it this way:

const Observable = require('zen-observable');
const spy = require('observable-calls')(Observable);

const f = spy((a, b) => a + b)
f.calls(3).subscribe({
  next: console.log,
  complete: () => console.log('complete')
});

f(1, 2); // {args: [1, 2], output: 3}
f(2, 3); // {args: [2, 3], output: 5}
f(3, 4); // {args: [3, 4], output: 7}
// complete
f(4, 5); // no more console output

The library was tested with zen-observable but any compliant Observable library should be usable.

The library module exports a function with the following signature: Observable => function => function

The first call specifies the Observable implementation library to use. The second call will transform any function in a new function with a calls property.

This calls property is a function providing a new Observable at each call. It takes an integer as its only argument in order to specify the number of calls to observe until completion.

The values that can be emitted by the Observable are:

• {args: [...], output: ...} in case of a successful function call;
• {args: [...], err: ...} in case of an exception raised by a function call.

If calls is called with no argument, the default number of calls to observe is 0 which means that the new Observable will immediately complete. If you want the Observable to never complete, pass Infinity as the calls argument.