Hello.
I'm trying to follow the game of life discovery testing by Justin Searls , with TypeScript.

I added the second test, without changing the code, and it passes:

test('one generation', () => {
    const seedWorld = new World()
    td.when(generatesSeedWorld.generate()).thenReturn(seedWorld)
    const seedWorldSecond = new World()

    simulatesConway.simulate(1, 1337)

    td.verify(outputsWorld.output(seedWorld))
    td.verify(outputsWorld.output(seedWorldSecond))
  })

Because seedWorld is at this moment exactly the same as seedWorldSecond (although it is not THE SAME one). When I added this.random = Math.random() to World constructor, the test properly failes.
I'm trying to understand the principle behind this kind of testing, which should not be language/framework specific as far as I understand.

How would you write a test like this then, in testdouble? Should I somehow force a different comparison mode? For now for learning purposes I'm going to leave the random there, but "there must be a better way" ;-)

Thanks a lot!