[TEST] add test for alphabet customisation point

test/unit/alphabet/CMakeLists.txt

@@ -1 +1,2 @@
 add_subdirectories()
+seqan3_test(custom_alphabet_test.cpp)

test/unit/alphabet/custom_alphabet_test.cpp

@@ -0,0 +1,69 @@
+// -----------------------------------------------------------------------------------------------------
+// Copyright (c) 2006-2019, Knut Reinert & Freie Universität Berlin
+// Copyright (c) 2016-2019, Knut Reinert & MPI für molekulare Genetik
+// This file may be used, modified and/or redistributed under the terms of the 3-clause BSD-License
+// shipped with this file and also available at: https://github.com/seqan/seqan3/blob/master/LICENSE.md
+// -----------------------------------------------------------------------------------------------------
+
+#include <seqan3/core/platform.hpp>
+#include <cereal/types/common.hpp>
+
+#include "alphabet_test_template.hpp"
+#include "alphabet_constexpr_test_template.hpp"
+
+// Tests the ADL-capabilities of the alphabet customisation point objects
+
+namespace my_namespace
+{
+
+enum class my_alph
+{
+    ZERO,
+    ONE,
+    TWO
+};
+
+constexpr size_t alphabet_size(my_alph const &) noexcept
+{
+    return 3;
+}
+
+constexpr size_t to_rank(my_alph const a) noexcept
+{
+    return static_cast<size_t>(a);
+}
+
+constexpr my_alph & assign_rank_to(size_t const r, my_alph & a) noexcept
+{
+    switch (r)
+    {
+        case 0:  a = my_alph::ZERO; return a;
+        case 1:  a = my_alph::ONE;  return a;
+        default: a = my_alph::TWO;  return a;
+    }
+}
+
+constexpr char to_char(my_alph const a) noexcept
+{
+    switch (a)
+    {
+        case my_alph::ZERO: return '0';
+        case my_alph::ONE:  return '1';
+        default:            return '2';
+    }
+}
+
+constexpr my_alph & assign_char_to(char const c, my_alph & a) noexcept
+{
+    switch (c)
+    {
+        case '0': a = my_alph::ZERO; return a;
+        case '1': a = my_alph::ONE;  return a;
+        default:  a = my_alph::TWO;  return a;
+    }
+}
+
+}
+
+INSTANTIATE_TYPED_TEST_CASE_P(my_alph, alphabet,            my_namespace::my_alph);
+INSTANTIATE_TYPED_TEST_CASE_P(my_alph, alphabet_constexpr,  my_namespace::my_alph);