Calculate execution time for a block of Swift code

executionTimeInterval.swift

// based on gist https://gist.github.com/kristopherjohnson/4201fbe86473f6edb207
// and discussion
// https://forums.swift.org/t/recommended-way-to-measure-time-in-swift/33326/4
// https://github.com/apple/swift-corelibs-xctest/pull/109

// Ensures Monotonic time
public func executionTimeInterval(block: () -> ()) -> TimeInterval {
    let start = Foundation.ProcessInfo.processInfo.systemUptime
    block();
    let end = Foundation.ProcessInfo.processInfo.systemUptime
    return end - start
}