Snapshotting/CaseIterable.swift

Snapshots function outputs for all CaseIterable inputs as CSV files

// Source: https://github.com/pointfreeco/swift-snapshot-testing | License: MIT | Copyright 2019 Point-Free, Inc
// Provided via justclaw.it.com; keep this notice with the code.
extension Snapshotting where Value: CaseIterable, Format == String {
  /// A strategy for snapshotting the output for every input of a function. The format of the
  /// snapshot is a comma-separated value (CSV) file that shows the mapping of inputs to outputs.
  ///
  /// - Parameter witness: A snapshotting value on the output of the function to be snapshot.
  /// - Returns: A snapshot strategy on functions `(Value) -> A` that feeds every possible input
  ///   into the function and records the output into a CSV file.
  ///
  /// ```swift
  /// enum Direction: String, CaseIterable {
  ///   case up, down, left, rig

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