Refactor single-program channel test to Boost.Test suites and cases

Motivation:
- state clearly what is covered with tests without reading non-trivial code
- avoid cleverness - tests should be no-brainer
- get closer to one test case targets one feature/beaviour with one check
- replace obscure `throw std::exception` with diagnostics that are actually
  useful to pin-point failure cause and location - makes CI logs useful.
- allow to select and run specific tests
- make tests maintenance easy, quick and fun

Propose new structure of tests that reflects the previous tests hierarchy,
but organizes channel tests in test/channel directory with test programs
each covering specific library feature (or set of closely related features).

The refactored tests cover 100% of checks from the old `channel.cpp`,
plus it refines or adds a bunch more.
NOTE: old test/channel.cpp has not been removed yet.

Common definitions from the single test/channel.cpp moved to
channel_test_fixtures.hpp and namespace boost::gil::test::fixture:
Classes and typedefs:
- `do_test` as `fixture::channel`
- `value_core` as `fixture::channel_value`
- `reference_core` as `fixture::channel_reference`
- `packed_reference_core` as `fixture::packed_channel_reference`
- `packed_dynamic_reference_core` as `fixture::packed_dynamic_channel_reference`
- `channel_archetype` and relatives to `channel_concepts.cpp` which is compile
   test in Jamfile
- `test_packed_channel_reference()` parts as `fixture::packed_channels565`
- `test_packed_dynamic_channel_reference()` parts as `fixture::packed_dynamic_channels565`
Test case functions called from `do_test<T>::test_all`:
- `test_channel_invert()` to `algorithm_channel_invert.cpp` suite
- `test_channel_convert()` to `algorithm_channel_convert.cpp` suite
- `test_channel_multiply()` to `algorithm_channel_multiply.cpp` suite
- `test_channel_math()` split to `algorithm_channel_relation.cpp`
   and `algorithm_channel_arithmetic.cpp`

Add test cases for each channel value type T as used to run from
`test_channel_value_impl<T>`, `test_packed_channel_reference<T>` and
`test_packed_dynamic_channel_reference<T>`.

Add list of possible T-s defined as type-lists `fixture::channel_byte_types`,
`fixture::channel_integer_types`, `channel_float_types` and
`channel_bitfield_types` which used with `BOOST_AUTO_TEST_CASE_TEMPLATE`
generate all possible combination of inputs.

Add new `channel_test_fixture.cpp` is a self-test suite verifying the fixtures.

test/channel/algorithm_channel_convert.cpp

@@ -0,0 +1,115 @@
+//
+// Copyright 2005-2007 Adobe Systems Incorporated
+// Copyright 2018 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/channel_algorithm.hpp>
+#include <cstdint>
+
+#define BOOST_TEST_MODULE test_algorithm_channel_convert
+#include <gil_test_common.hpp>
+#include "channel_test_fixture.hpp"
+
+namespace gil = boost::gil;
+namespace fixture = boost::gil::test::fixture;
+
+template <typename ChannelFixtureBase>
+struct test_convert_to
+{
+    using channel_t = typename fixture::channel<ChannelFixtureBase>::channel_t;
+    using channel_value_t = typename fixture::channel<ChannelFixtureBase>::channel_value_t;
+
+    template <typename Channel>
+    static void from(Channel src_min_v, Channel src_max_v)
+    {
+        channel_value_t min_v = gil::channel_convert<channel_t>(src_min_v);
+        channel_value_t max_v = gil::channel_convert<channel_t>(src_max_v);
+        fixture::channel_minmax_value<channel_value_t> expect;
+        BOOST_TEST(min_v == expect.min_v_);
+        BOOST_TEST(max_v == expect.max_v_);
+    }
+};
+
+//--- Test gil::channel_convert from integral channels to all byte channels -------------
+#define GIL_TEST_CHANNEL_CONVERT_FROM(source_channel_type) \
+    BOOST_FIXTURE_TEST_SUITE( \
+        channel_convert_from_##source_channel_type, \
+        fixture::channel_minmax_value<std::source_channel_type>) \
+    BOOST_AUTO_TEST_CASE_TEMPLATE(channel_value, Channel, fixture::channel_byte_types) \
+    {   test_convert_to<fixture::channel_value<Channel>>::from(min_v_, max_v_); } \
+    BOOST_AUTO_TEST_CASE_TEMPLATE(channel_reference, Channel, fixture::channel_byte_types) \
+    {   test_convert_to<fixture::channel_reference<Channel&>>::from(min_v_, max_v_); } \
+    BOOST_AUTO_TEST_CASE_TEMPLATE(channel_reference_const, Channel, fixture::channel_byte_types) \
+    {   test_convert_to<fixture::channel_reference<Channel const&>>::from(min_v_, max_v_); } \
+    BOOST_AUTO_TEST_CASE(packed_channel_reference) \
+    { \
+        using channels565_t = fixture::packed_channels565<std::uint16_t>; \
+        test_convert_to<typename channels565_t::fixture_0_5_t>::from(min_v_, max_v_); \
+        test_convert_to<typename channels565_t::fixture_5_6_t>::from(min_v_, max_v_); \
+        test_convert_to<typename channels565_t::fixture_11_5_t>::from(min_v_, max_v_); \
+    } \
+    BOOST_AUTO_TEST_CASE(packed_dynamic_channel_reference) \
+    { \
+        using channels565_t = fixture::packed_dynamic_channels565<std::uint16_t>; \
+        test_convert_to<typename channels565_t::fixture_5_t>::from(min_v_, max_v_); \
+        test_convert_to<typename channels565_t::fixture_6_t>::from(min_v_, max_v_); \
+    } \
+    BOOST_AUTO_TEST_SUITE_END()
+
+GIL_TEST_CHANNEL_CONVERT_FROM(uint8_t)
+GIL_TEST_CHANNEL_CONVERT_FROM(int8_t)
+GIL_TEST_CHANNEL_CONVERT_FROM(uint16_t)
+GIL_TEST_CHANNEL_CONVERT_FROM(int16_t)
+GIL_TEST_CHANNEL_CONVERT_FROM(uint32_t)
+GIL_TEST_CHANNEL_CONVERT_FROM(int32_t)
+
+#undef GIL_TEST_CHANNEL_CONVERT_FROM
+
+// FIXME: gil::float32_t <-> gil::float64_t seems not supported
+
+//--- Test gil::channel_convert from gil::float32_t to all integer channels -------------
+BOOST_FIXTURE_TEST_SUITE(channel_convert_from_float32_t,
+                         fixture::channel_minmax_value<gil::float32_t>)
+
+BOOST_AUTO_TEST_CASE_TEMPLATE(channel_value, Channel, fixture::channel_integer_types)
+{
+    test_convert_to<fixture::channel_value<Channel>>::from(min_v_, max_v_);
+}
+
+BOOST_AUTO_TEST_CASE_TEMPLATE(channel_reference, Channel, fixture::channel_integer_types)
+{
+    test_convert_to<fixture::channel_reference<Channel&>>::from(min_v_, max_v_);
+}
+
+BOOST_AUTO_TEST_CASE_TEMPLATE(
+    channel_reference_const, Channel, fixture::channel_integer_types)
+{
+    test_convert_to<fixture::channel_reference<Channel const&>>::from(min_v_, max_v_);
+}
+
+BOOST_AUTO_TEST_SUITE_END()
+
+//--- Test gil::channel_convert from gil::float64_t to all integer channels -------------
+BOOST_FIXTURE_TEST_SUITE(channel_convert_from_float64_t,
+                         fixture::channel_minmax_value<gil::float64_t>)
+
+BOOST_AUTO_TEST_CASE_TEMPLATE(channel_value, Channel, fixture::channel_integer_types)
+{
+    test_convert_to<fixture::channel_value<Channel>>::from(min_v_, max_v_);
+}
+
+BOOST_AUTO_TEST_CASE_TEMPLATE(channel_reference, Channel, fixture::channel_integer_types)
+{
+    test_convert_to<fixture::channel_reference<Channel&>>::from(min_v_, max_v_);
+}
+
+BOOST_AUTO_TEST_CASE_TEMPLATE(
+    channel_reference_const, Channel, fixture::channel_integer_types)
+{
+    test_convert_to<fixture::channel_reference<Channel const&>>::from(min_v_, max_v_);
+}
+
+BOOST_AUTO_TEST_SUITE_END()