StdlibUnittest: add checkStrideable()

Author: gribozavr

stdlib/private/StdlibUnittest/CMakeLists.txt

@@ -15,6 +15,7 @@ add_swift_library(swiftStdlibUnittest ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} IS_STD
   # filename.
   StdlibUnittest.swift.gyb
 
+  CheckStrideable.swift.gyb
   InspectValue.cpp
   InspectValue.swift
   InterceptTraps.cpp

stdlib/private/StdlibUnittest/CheckStrideable.swift.gyb

@@ -0,0 +1,32 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+%{
+from gyb_stdlib_unittest_support import TRACE, stackTrace, trace
+}%
+
+public func checkStrideable<S : Strideable>(
+  instances: [S],
+  distances: [S.Stride],
+  distanceOracle: (Int, Int) -> S.Stride,
+  ${TRACE}
+) {
+  for i in instances.indices {
+    let first = instances[i]
+    for j in instances.indices {
+      let second = instances[j]
+      expectEqual(distanceOracle(i, j), first.distance(to: second))
+      expectEqual(second, first.advanced(by: distanceOracle(i, j)))
+    }
+  }
+}
+