[Test] Add a test for rdar://problem/46685973

Author: DougGregor

test/Runtime/conformance_uniquing.swift

@@ -0,0 +1,20 @@
+// RUN: %target-run-simple-swift
+// REQUIRES: executable_test
+// REQUIRES: objc_interop
+
+import StdlibUnittest
+import Foundation
+
+let conformanceUniquingTests = TestSuite("ConformanceUniquing")
+
+func isSimpleSetAlgebra<T: SetAlgebra>(_: T.Type) -> Bool {
+  return T.self == T.Element.self
+}
+
+// rdar://problem/46685973
+conformanceUniquingTests.test("Nested types with the same name") {
+  expectTrue(isSimpleSetAlgebra(NSData.WritingOptions.self))
+  expectTrue(isSimpleSetAlgebra(JSONSerialization.WritingOptions.self))
+}
+
+runAllTests()