Add test for some bit-aligned pixel types and metafunctions (#257)

Test bit_aligned_pixel_reference and packed_pixel as well as
some of related metafunctions generating types of their
members and intermediate specializations.

test/pixel/bit_aligned_pixel_reference.cpp

@@ -0,0 +1,46 @@
+//
+// Copyright 2019 Mateusz Loskot <mateusz at loskot dot net>
+//
+// Distributed under the Boost Software License, Version 1.0
+// See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt
+//
+#include <boost/gil/bit_aligned_pixel_reference.hpp>
+#include <boost/gil/packed_pixel.hpp>
+#include <boost/gil/rgb.hpp>
+#include <boost/mpl/vector_c.hpp>
+namespace gil = boost::gil;
+namespace mpl = boost::mpl;
+
+int main()
+{
+    using bgr121_ref_t = gil::bit_aligned_pixel_reference
+        <
+            std::uint8_t, mpl::vector3_c<int, 1, 2, 1>, gil::bgr_layout_t, true
+        >;
+
+    static_assert(bgr121_ref_t::bit_size == 4,
+        "bit size should be 4");
+
+    static_assert(std::is_same<bgr121_ref_t::bitfield_t, std::uint8_t>::value,
+        "bit field type should be std::uint8_t");
+
+    static_assert(std::is_same<bgr121_ref_t::layout_t, gil::bgr_layout_t>::value,
+        "layout type should be bgr");
+
+    static_assert(std::is_same<decltype(bgr121_ref_t::is_mutable), bool const>::value &&
+        bgr121_ref_t::is_mutable,
+        "is_mutable should be boolean");
+
+    using packed_pixel_t = gil::packed_pixel
+        <
+            std::uint8_t,
+            typename gil::detail::packed_channel_references_vector_type
+            <
+                std::uint8_t, mpl::vector3_c<int, 1, 2, 1>
+            >::type,
+            gil::bgr_layout_t
+        >;
+    static_assert(std::is_same<bgr121_ref_t::value_type, packed_pixel_t >::value,
+        "value_type should be specialization of packed_pixel");
+}