Swift: Add a test for UITextField.

swift/ql/test/library-tests/dataflow/flowsources/uikit.swift

@@ -0,0 +1,30 @@
+// --- stubs ---
+
+class NSObject { }
+class NSAttributedString: NSObject {}
+class UIResponder: NSObject {}
+class UIView: UIResponder {}
+class UIControl: UIView {}
+class UITextField: UIControl {
+  var text: String? {
+    get { nil }
+    set { }
+  }
+  var attributedText: NSAttributedString? {
+    get { nil }
+    set { }
+  }
+  var placeholder: String? {
+    get { nil }
+    set { }
+  }
+}
+
+// --- tests ---
+
+func testUITextField(textField: UITextField) {
+  _ = textField.text // $ MISSING: source=local
+  _ = textField.attributedText // $ MISSING: source=local
+  _ = textField.placeholder // GOOD (not input)
+  _ = textField.text?.uppercased() // $ MISSING: source=local
+}