Fixes #993. More Union tests for FFI library added

Author: sgrekhov

LibTest/ffi/Array/UnionArray_A01_t01.dart

@@ -0,0 +1,61 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion
+/// const Array<T extends NativeType>(
+/// int dimension1,
+///  [int dimension2,
+///  int dimension3,
+///  int dimension4,
+///  int dimension5]
+///  )
+///  Const constructor to specify Array dimensions in Structs.
+///
+///  class MyStruct extends Struct {
+///  @Array(8)
+///  external Array<Uint8> inlineArray;
+///
+///  @Array(2, 2, 2)
+///  external Array<Array<Array<Uint8>>> threeDimensionalInlineArray;
+///  }
+///  Do not invoke in normal code.
+///
+/// @description Checks that this class represents a fixed-size array of Pointer
+/// @author [email protected]
+
+import "dart:ffi";
+import "package:ffi/ffi.dart";
+import "../../../Utils/expect.dart";
+
+class Coord extends Union {
+  @Double()
+  external double x;
+  @Double()
+  external double y;
+}
+
+class MyStruct extends Struct {
+  @Array(2)
+  external Array<Coord> a0;
+}
+
+void main() {
+  final pointer = calloc<MyStruct>();
+  try {
+    final array = pointer.ref.a0;
+    for (int i = 0; i < 2; i++) {
+      Expect.equals(0, array[i].x);
+      Expect.equals(0, array[i].y);
+      array[i].x = 42;
+      array[i].y = 3.14;
+      Expect.equals(3.14, array[i].x);
+      Expect.equals(3.14, array[i].y);
+      array[i].x = 42;
+      Expect.equals(42, array[i].x);
+      Expect.equals(42, array[i].y);
+    }
+  } finally {
+    calloc.free(pointer);
+  }
+}

LibTest/ffi/Union/Union_A08_t01.dart

@@ -0,0 +1,48 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion Field declarations in a Union subclass declaration are
+/// automatically given a setter and getter implementation which accesses the
+/// native union's field in memory.
+///
+/// @description Checks that fields in a Union subclass shares the same memory
+/// @author [email protected]
+
+import "dart:ffi";
+import "package:ffi/ffi.dart";
+import "../../../Utils/expect.dart";
+
+class U extends Union {
+  @Int32()
+  external int x;
+
+  @Int16()
+  external int y;
+}
+
+void main() {
+  Pointer<U> p = calloc<U>();
+  U u = p.ref;
+  u.y = -42;
+  u.x = 42;
+  Expect.equals(42, u.x);
+  Expect.equals(42, u.y);
+
+  u.x = 1;
+  u.y = 2;
+  Expect.equals(2, u.x);
+  Expect.equals(2, u.y);
+
+  u.x = 65537;
+  Expect.equals(65537, u.x);
+  Expect.equals(1, u.y);
+
+  u.x = 65538;
+  Expect.equals(65538, u.x);
+  Expect.equals(2, u.y);
+
+  u.y = 2;
+  Expect.equals(65538, u.x);
+  Expect.equals(2, u.y);
+}