Code from README doesn't compile

[xavierLowmiller]

Version

077c096c3ddfc38db223ac8e525ad16ffb987138

Environment

macOS 10.15.6, Swift 5.2, Xcode 11.6

Description

I was following the steps from README.md to learn about SwiftCheck.
Unfortunately, the example for complex properties doesn't compile:

property("Shrunken lists of integers always contain [] or [0]") <- forAll { (l : [Int]) in
  // Here we use the Implication Operator `==>` to define a precondition for
  // this test.  If the precondition fails the test is discarded.  If it holds
  // the test proceeds.
  return (!l.isEmpty && l != [0]) ==> {
    let ls = self.shrinkArbitrary(l)
    //       ^ Value of type 'ExampleTests' has no member 'shrinkArbitrary'
    return (ls.filter({ $0 == [] || $0 == [0] }).count >= 1)
  }
}

I'm no expert on QuickCheck (or SwiftCheck), so I don't know how to fix this message.

Steps To Reproduce

1. Create a new test function
2. Copy the code block from README.md

Expected Result

The code compiles and produces a passing test case.

Actual Result

There is a compiler error:
Value of type 'ExampleTests' has no member 'shrinkArbitrary'

Additional information

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