Added layer cake patter

tests/t00019/t00019_layer3.h

@@ -0,0 +1,33 @@
+#pragma once
+
+#include <string>
+
+namespace clanguml {
+namespace t00019 {
+
+template <typename LowerLayer> class Layer3 : public LowerLayer {
+
+    using LowerLayer::LowerLayer;
+
+    virtual int m1() override
+    {
+        m_m1_calls++;
+        return LowerLayer::m1();
+    }
+
+    virtual std::string m2() override
+    {
+        m_m2_calls++;
+        return LowerLayer::m2();
+    }
+
+    int m1_calls() const { return m_m1_calls; }
+
+    int m2_calls() const { return m_m2_calls; }
+
+private:
+    int m_m1_calls{};
+    int m_m2_calls{};
+};
+}
+}