Added tests for mirroring functions

Test/MirrorHorizontally.cpp

@@ -0,0 +1,39 @@
+#include <Bmp.h>
+#include <stdexcept>
+#include "Catch2.h"
+
+using namespace Leonetienne::BmpPP;
+using namespace Eule;
+
+// Tests the mirror horizontal function against reference images
+TEST_CASE(__FILE__"/Mirroring produces the correct results", "[Mirroring][MirrorHorizontally]")
+{
+    SECTION("RGB") {
+        // Read a gradient image
+        BMP bmp("base_gradient.bmp");
+
+        // Mirror it
+        bmp = bmp.MirrorHorizontally();
+
+        // Read reference image
+        const BMP reference("base_gradient_flipped_hor.bmp");
+
+        // Assert that they are equal
+        REQUIRE(bmp == reference);
+    }
+
+    SECTION("RGBA") {
+        // Read a gradient image
+        BMP bmp("basea_gradient.bmp");
+
+        // Mirror it
+        bmp = bmp.MirrorHorizontally();
+
+        // Read reference image
+        const BMP reference("basea_gradient_flipped_hor.bmp");
+
+        // Assert that they are equal
+        REQUIRE(bmp == reference);
+    }
+    return;
+}