Added implementatino of color conversion method, and added tests

Test/CMakeLists.txt

@@ -29,6 +29,7 @@ add_executable(Test
         MirrorVertically.cpp
         SwapChannels.cpp
         Rotate.cpp
+        ConvertColormode.cpp
 )
 
 # Move test images to build dir

Test/ConvertColormode.cpp

@@ -0,0 +1,68 @@
+#include <Bmp.h>
+#include <stdexcept>
+#include "Catch2.h"
+
+using namespace Leonetienne::BmpPP;
+using namespace Eule;
+
+// Tests converting between color modes works
+TEST_CASE(__FILE__"/Converting_between_color_modes_works", "[Conversion]")
+{
+    SECTION("RGB to RGB") {
+        // Read an RGB image
+        BMP bmp("base_kyokucho.bmp");
+
+        // Convert it to RGB
+        bmp.ConvertColormode(Colormode::RGB);
+
+        // Read reference image
+        const BMP reference("base_kyokucho.bmp");
+
+        // Assert that they are equal
+        REQUIRE(bmp == reference);
+    }
+
+    SECTION("RGB to RGBA") {
+        // Read an RGB image
+        BMP bmp("base_kyokucho.bmp");
+
+        // Convert it to RGBA
+        bmp.ConvertColormode(Colormode::RGBA);
+
+        // Read reference image
+        const BMP reference("basea_kyokucho.bmp");
+
+        // Assert that they are equal
+        REQUIRE(bmp == reference);
+    }
+
+    SECTION("RGBA to RGB") {
+        // Read an RGBA image
+        BMP bmp("basea_kyokucho.bmp");
+
+        // Convert it to RGB
+        bmp.ConvertColormode(Colormode::RGB);
+
+        // Read reference image
+        const BMP reference("base_kyokucho.bmp");
+
+        // Assert that they are equal
+        REQUIRE(bmp == reference);
+    }
+
+    SECTION("RGBA to RGBA") {
+        // Read an RGBA image
+        BMP bmp("basea_kyokucho.bmp");
+
+        // Convert it to RGBA
+        bmp.ConvertColormode(Colormode::RGBA);
+
+        // Read reference image
+        const BMP reference("basea_kyokucho.bmp");
+
+        // Assert that they are equal
+        REQUIRE(bmp == reference);
+    }
+
+    return;
+}