diff --git a/src/tools/std20/concepts/test/CMakeLists.txt b/src/tools/std20/concepts/test/CMakeLists.txt
index 7bcf7d0..65b93b7 100644
--- a/src/tools/std20/concepts/test/CMakeLists.txt
+++ b/src/tools/std20/concepts/test/CMakeLists.txt
@@ -1,2 +1,5 @@
+add_cpp_test( std20.concepts.convertible_to        convertible_to.test.cpp )
+add_cpp_test( std20.concepts.derived_from          derived_from.test.cpp )
 add_cpp_test( std20.concepts.equality_comparable   equality_comparable.test.cpp )
+add_cpp_test( std20.concepts.same_as               same_as.test.cpp )
 add_cpp_test( std20.concepts.totally_ordered       totally_ordered.test.cpp )
diff --git a/src/tools/std20/concepts/test/convertible_to.test.cpp b/src/tools/std20/concepts/test/convertible_to.test.cpp
new file mode 100644
index 0000000..ea5bf8a
--- /dev/null
+++ b/src/tools/std20/concepts/test/convertible_to.test.cpp
@@ -0,0 +1,30 @@
+// include Catch2
+#include <catch2/catch_test_macros.hpp>
+
+// what we are testing
+#include "tools/std20/concepts.hpp"
+
+// other includes
+
+// convenience typedefs
+//using namespace njoy::tools;
+namespace std20 = nano::ranges;
+
+// test code
+struct Foo {};
+
+struct Bar : public Foo {};
+
+struct AlsoBar : private Foo {};
+
+SCENARIO( "derived_from" ) {
+
+  CHECK( std20::convertible_to< Foo, Foo > );
+  CHECK( std20::convertible_to< Bar, Foo > );
+  CHECK( std20::convertible_to< int, double > );
+  CHECK( std20::convertible_to< double, int > );
+  CHECK( std20::convertible_to< void, void > );
+
+  CHECK( ! std20::convertible_to< Foo, Bar > );       // Foo is not derived from Bar
+  CHECK( ! std20::convertible_to< AlsoBar, Foo > );   // private inheritance from Bar
+} // SCENARIO
diff --git a/src/tools/std20/concepts/test/derived_from.test.cpp b/src/tools/std20/concepts/test/derived_from.test.cpp
new file mode 100644
index 0000000..9559837
--- /dev/null
+++ b/src/tools/std20/concepts/test/derived_from.test.cpp
@@ -0,0 +1,30 @@
+// include Catch2
+#include <catch2/catch_test_macros.hpp>
+
+// what we are testing
+#include "tools/std20/concepts.hpp"
+
+// other includes
+
+// convenience typedefs
+//using namespace njoy::tools;
+namespace std20 = nano::ranges;
+
+// test code
+struct Foo {};
+
+struct Bar : public Foo {};
+
+struct AlsoBar : private Foo {};
+
+SCENARIO( "derived_from" ) {
+
+  CHECK( std20::derived_from< Foo, Foo > );
+  CHECK( std20::derived_from< Bar, Foo > );
+
+  CHECK( ! std20::derived_from< int, double > );    // different primitive types
+  CHECK( ! std20::derived_from< int, int > );       // same primitive types
+  CHECK( ! std20::derived_from< double, double > ); // same primitive types
+  CHECK( ! std20::derived_from< Foo, Bar > );       // Foo is not derived from Bar
+  CHECK( ! std20::derived_from< AlsoBar, Foo > );   // private inheritance from Bar
+} // SCENARIO
diff --git a/src/tools/std20/concepts/test/same_as.test.cpp b/src/tools/std20/concepts/test/same_as.test.cpp
new file mode 100644
index 0000000..3d715bd
--- /dev/null
+++ b/src/tools/std20/concepts/test/same_as.test.cpp
@@ -0,0 +1,30 @@
+// include Catch2
+#include <catch2/catch_test_macros.hpp>
+
+// what we are testing
+#include "tools/std20/concepts.hpp"
+
+// other includes
+
+// convenience typedefs
+//using namespace njoy::tools;
+namespace std20 = nano::ranges;
+
+// test code
+struct Foo {};
+
+struct Bar {};
+
+SCENARIO( "same_as" ) {
+
+  CHECK( std20::same_as< int, int > );
+  CHECK( std20::same_as< double, double > );
+  CHECK( std20::same_as< Foo, Foo > );
+
+  CHECK( std20::same_as< std::common_type_t< int, int, int >, int > );
+  CHECK( std20::same_as< std::common_type_t< int, float, double >, double > );
+
+  CHECK( ! std20::same_as< double, int > );
+  CHECK( ! std20::same_as< int, double > );
+  CHECK( ! std20::same_as< Foo, Bar > );
+} // SCENARIO