Add tests for ColourGuard

tests/SelfTest/IntrospectiveTests/ColourImpl.tests.cpp

@@ -0,0 +1,63 @@
+
+//              Copyright Catch2 Authors
+// Distributed under the Boost Software License, Version 1.0.
+//   (See accompanying file LICENSE_1_0.txt or copy at
+//        https://www.boost.org/LICENSE_1_0.txt)
+
+// SPDX-License-Identifier: BSL-1.0
+
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/internal/catch_console_colour.hpp>
+
+#include <sstream>
+
+namespace {
+    class TestColourImpl : public Catch::ColourImpl {
+        using Catch::ColourImpl::ColourImpl;
+        // Inherited via ColourImpl
+        void use( Catch::Colour::Code colourCode ) const override {
+            m_stream->stream() << "Using code: " << colourCode << '\n';
+        }
+    };
+
+    class TestStringStream : public Catch::IStream {
+        mutable std::stringstream m_stream;
+    public:
+        std::ostream& stream() const override {
+            return m_stream;
+        }
+
+        std::string str() const { return m_stream.str(); }
+    };
+}
+
+TEST_CASE("ColourGuard behaviour", "[console-colours]") {
+    TestStringStream streamWrapper;
+    TestColourImpl colourImpl( &streamWrapper );
+    auto& stream = streamWrapper.stream();
+
+    SECTION("ColourGuard is disengaged by default") {
+        { auto guard = colourImpl.guardColour( Catch::Colour::Red ); }
+
+        REQUIRE( streamWrapper.str().empty() );
+    }
+
+    SECTION("ColourGuard is engaged by op<<") {
+        stream << "1\n" << colourImpl.guardColour( Catch::Colour::Red ) << "2\n";
+        stream << "3\n";
+
+        REQUIRE( streamWrapper.str() == "1\nUsing code: 2\n2\nUsing code: 0\n3\n" );
+    }
+
+    SECTION("ColourGuard can be engaged explicitly") {
+        {
+            auto guard =
+                colourImpl.guardColour( Catch::Colour::Red ).engage( stream );
+            stream << "A\n"
+                   << "B\n";
+        }
+        stream << "C\n";
+        REQUIRE( streamWrapper.str() ==
+                 "Using code: 2\nA\nB\nUsing code: 0\nC\n" );
+    }
+}