Provide global parameters definition

[BourgoisMickael]

🚀 Feature Request

Provide a way to define parameters on fc rather than defining them in each fc.check or fc.assert.

Motivation

I'm using the same parameter { verbose: true } for each call of fc.check and I'd like to provide it only once for all my tests

Example

fc.setParameter({ verbose: true })

fc.assert(
  fc.property(
    fc.integer(), num => { throw new Error(num) }
  ),
  // { verbose: true } No need to define the parameter here
)

Right now to achieve this behavior, I'm doing something like this:

  const fcCheck = fc.check
  const fcAssert = fc.assert

  function wrapCheck (property, param = { verbose: true }) {
    return fcCheck(property, param)
  }

  function wrapAssert (property, param = { verbose: true }) {
    fcAssert(property, param)
  }

  fc.check = wrapCheck
  fc.assert = wrapAssert

[dubzzz]

There is definitely a need for such feature. When I first though about this kind of feature I opened #65.

Your suggestion is a bit different as it suggests to put the configuration in the code itself (instead of env in the other issue) but in a way they both fulfill the same need.

The only blocking point I see with such is that it makes the behaviour of fc.assert and fc.check dependant of its execution context.

• What would be the behaviour of?

fc.setParameters({ verbose: 1 })
fc.assert(fc.property(fc.boolean(), b => true), { seed: 42 })
// do we consider { seed: 42 } or { seed: 42, verbose: 1 }?
// IMO the second one seems better

• Do we allow to set anything with fc.setParameters or only a subset?
  For instance: replayPath is very specific to one fc.assert while seed, numRuns or verbose can be set globally.

• How do we make the user knowledgeable that her fc.assert settings have been tweaked by a global configuration? Do we make the user aware of the fact that we took the configuration from a global?

Before implementing such I'll need to check how other big libraries or test frameworks deal with such global configurations that can be set both at test level and global level.

[dubzzz]

@BourgoisMickael I just worked a bit on this feature request, see #439

After that commit a code like:

test('test #1', () => {
  fc.assert(
    myProp1,
    { numRuns: 10 }
  )
})
test('test #2', () => {
  fc.assert(
    myProp2,
    { numRuns: 10 } // duplicated
  )
})
test('test #3', () => {
  fc.assert(
    myProp3,
    { numRuns: 10 } // duplicated
  )
})

Can be written:

fc.configureGlobal({ numRuns: 10 })
test('test #1', () => {
  fc.assert(myProp1)
})
test('test #2', () => {
  fc.assert(myProp2)
})
test('test #3', () => {
  fc.assert(myProp3)
})

In the case of Jest test runner, the call to configureGlobal can be extracted into setupFiles option of Jest so that it will apply to all specs.

With this PR I add three main functions (the first one is certainly the most important one):

• fc.configureGlobal(parameters: Parameters): define the default parameters to be used by runners
• fc.resetConfigureGlobal(): reset the default parameters to be used by runners
• fc.readConfigureGlobal(): output the default parameters to be used by runners

What do you think of this feature? Naming, usage...?