diff --git a/polymorphism/include/polymorphism/consume_class_that_adheres_to_concept.hpp b/polymorphism/include/polymorphism/consume_class_that_adheres_to_concept.hpp
index 4a7f695..fe09c36 100644
--- a/polymorphism/include/polymorphism/consume_class_that_adheres_to_concept.hpp
+++ b/polymorphism/include/polymorphism/consume_class_that_adheres_to_concept.hpp
@@ -1,5 +1,5 @@
-#ifndef POYMORPHISM_CONSUME_CLASS_THAT_ADHERES_TO_CONCEPT_HPP
-#define POYMORPHISM_CONSUME_CLASS_THAT_ADHERES_TO_CONCEPT_HPP
+#ifndef POLYMORPHISM_CONSUME_CLASS_THAT_ADHERES_TO_CONCEPT_HPP
+#define POLYMORPHISM_CONSUME_CLASS_THAT_ADHERES_TO_CONCEPT_HPP
 
 #include <polymorphism/has_super_cool_features.hpp>
 
@@ -12,4 +12,4 @@ std::string consume(has_super_cool_features auto& s);
 
 } // namespace modern
 
-#endif // POYMORPHISM_CONSUME_CLASS_THAT_ADHERES_TO_CONCEPT_HPP
\ No newline at end of file
+#endif // POLYMORPHISM_CONSUME_CLASS_THAT_ADHERES_TO_CONCEPT_HPP
\ No newline at end of file
diff --git a/polymorphism/test/CMakeLists.txt b/polymorphism/test/CMakeLists.txt
index d351f0c..c40aef7 100644
--- a/polymorphism/test/CMakeLists.txt
+++ b/polymorphism/test/CMakeLists.txt
@@ -15,17 +15,24 @@ add_library(polymorphism_lib
 )
 
 target_compile_features(polymorphism_lib PUBLIC cxx_std_23)
-target_include_directories(polymorphism_lib PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/../include)
-target_include_directories(polymorphism_lib PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/../src)
+target_include_directories(polymorphism_lib
+    PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/../include
+    PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/../src)
 
 add_executable(test_consume
-    test_consume.cpp
+    src/test_consume.cpp
+    src/mocking.cpp
 )
 
 target_compile_features(test_consume PUBLIC cxx_std_23)
-
-target_include_directories(test_consume PUBLIC ../include)
-target_include_directories(test_consume PUBLIC "${ut_SOURCE_DIR}")
+target_include_directories(test_consume
+    PRIVATE
+    # Library includes
+    ${CMAKE_CURRENT_SOURCE_DIR}/../include
+    ${CMAKE_CURRENT_SOURCE_DIR}/../src
+    # Test includes
+    ${CMAKE_CURRENT_SOURCE_DIR}/include
+    "${ut_SOURCE_DIR}")
 
 target_link_libraries(test_consume PRIVATE polymorphism_lib)
 
diff --git a/polymorphism/test/include/test_polymorphism/mocking.hpp b/polymorphism/test/include/test_polymorphism/mocking.hpp
new file mode 100644
index 0000000..d93f1f7
--- /dev/null
+++ b/polymorphism/test/include/test_polymorphism/mocking.hpp
@@ -0,0 +1,45 @@
+#ifndef POLYMORPHISM_MOCKING_HPP
+#define POLYMORPHISM_MOCKING_HPP
+
+#include <atomic>
+#include <cstddef>
+#include <list>
+#include <string>
+
+namespace mocking {
+
+struct Mock {
+    std::list<std::string> collectedSetArguments;
+    mutable std::atomic<std::size_t> numberOfCallsToCoolFeature { 0 };
+
+    /**
+     * @brief Returns the last set value or a default value if none exists.
+     * @note Thread-safe. Multiple concurrent calls are safe.
+     * @return The last set string or "<default value>" if no strings were set
+     */
+    std::string coolFeature() const
+    {
+        ++numberOfCallsToCoolFeature;
+
+        return collectedSetArguments.empty()
+            ? "<default value>"
+            : collectedSetArguments.back();
+    }
+
+    /**
+     * @brief Stores a string value for later retrieval by coolFeature
+     * @param s The string to store (must not be empty)
+     * @throws std::invalid_argument if the string is empty
+     */
+    void set(std::string s)
+    {
+        if (s.empty()) {
+            throw std::invalid_argument("Empty strings are not allowed");
+        }
+        collectedSetArguments.emplace_back(std::move(s));
+    }
+};
+
+} // namespace mocking
+
+#endif // POLYMORPHISM_MOCKING_HPP
\ No newline at end of file
diff --git a/polymorphism/test/src/mocking.cpp b/polymorphism/test/src/mocking.cpp
new file mode 100644
index 0000000..9089aeb
--- /dev/null
+++ b/polymorphism/test/src/mocking.cpp
@@ -0,0 +1,7 @@
+#include <consume_class_that_adheres_to_concept.ipp>
+#include <test_polymorphism/mocking.hpp>
+
+#include <string>
+
+// explicit instantiation of consume() for Mock
+template std::string modern::consume<mocking::Mock>(mocking::Mock&);
diff --git a/polymorphism/test/test_consume.cpp b/polymorphism/test/src/test_consume.cpp
similarity index 57%
rename from polymorphism/test/test_consume.cpp
rename to polymorphism/test/src/test_consume.cpp
index 1d7f51b..29ad7b7 100644
--- a/polymorphism/test/test_consume.cpp
+++ b/polymorphism/test/src/test_consume.cpp
@@ -5,6 +5,8 @@
 #include <polymorphism/impl_with_interface.hpp>
 #include <polymorphism/impl_without_interface.hpp>
 
+#include <test_polymorphism/mocking.hpp>
+
 int main()
 {
     using namespace boost::ut;
@@ -43,4 +45,31 @@ int main()
                   };
               };
           };
+
+    "[modern mock]"_test = [] {
+        static constexpr auto EXPECTED_COOLFEATURE_CALLS = 2; // coolFeature() is called:
+                                                              // 1. During initial value check (line 56)
+                                                              // 2. During side effect verification (line 70)
+        given("I have a an mock that adheres to a concept") = [] {
+            mocking::Mock impl;
+
+            expect("<default value>"s == impl.coolFeature());
+
+            when("I pass it to a function that expects an argument that fulfils the constraints") = [&] {
+                auto result = modern::consume(impl);
+
+                then("set() should be called twice") = [&] {
+                    expect(EXPECTED_COOLFEATURE_CALLS == impl.numberOfCallsToCoolFeature);
+                };
+
+                then("the answer to all questions should be given") = [=] {
+                    expect("The answer to all questions is 42"s == result);
+                };
+
+                then("the state of the argument should be modified as a side effect") = [&] {
+                    expect("42"s == impl.coolFeature());
+                };
+            };
+        };
+    };
 }