[cxx-interop] Add tests for the available operations of std::iterator

Author: cabmeurer

test/Interop/Cxx/stdlib/use-std-iterator.swift

@@ -0,0 +1,37 @@
+// RUN: %target-run-simple-swift(-I %S/Inputs -Xfrontend -enable-experimental-cxx-interop)
+//
+// REQUIRES: executable_test
+//
+// Enable this everywhere once we have a solution for modularizing libstdc++: rdar://87654514
+// REQUIRES: OS=macosx
+
+import StdlibUnittest
+import StdVector
+import std.vector
+
+var StdIteratorTestSuite = TestSuite("StdIterator")
+
+StdIteratorTestSuite.test("init") {
+    var vector = Vector()
+    var _1: CInt = 1
+    //There seems to be an issue when importing this method, where the const_ref is mapped with 
+    //the correct typealias to be able to pass immutable values. related to: https://github.com/apple/swift/pull/41611
+    vector.push_back(&_1)
+    //ideally we should call vector.begin(), however we need to prevent a copy of self before vector.begin() is invoked
+    //current workaround is to use beginMutating()
+    let it = vector.beginMutating()
+    expectEqual(it[0], 1)
+}
+
+StdIteratorTestSuite.test("advance") {
+    var vector = Vector()
+    var _1: CInt = 1, _2: CInt = 2, _3: CInt = 3
+    vector.push_back(&_1)
+    vector.push_back(&_2)
+    vector.push_back(&_3)
+    var it = vector.beginMutating()
+    std.__1.advance(&it, 2)
+    expectEqual(it[0], 3)
+}
+
+runAllTests()