diff --git a/sketch.cpp b/sketch.cpp
index 016de22..f01f8b2 100644
--- a/sketch.cpp
+++ b/sketch.cpp
@@ -1160,90 +1160,6 @@ void user_eval_expression_as ()
     std::cout << "\n";
 }
 
-namespace user_2 {
-
-    struct number
-    {
-        double value;
-    };
-
-    number naxpy (number a, number x, number y)
-    { return number{a.value * x.value + y.value}; }
-
-#if 0
-    auto eval_expression_as (
-        bp17::expression<
-            bp17::expr_kind::plus,
-            bp17::expression<
-                bp17::expr_kind::multiplies,
-                term<number>,
-                term<number>
-            >,
-            term<number>
-        > const & expr,
-        boost::hana::basic_type<number>)
-    {
-        std::cout << "User naxpy!  ";
-        using namespace boost::hana::literals;
-        return naxpy(
-            expr.elements[0_c].elements[0_c].elements[0_c],
-            expr.elements[0_c].elements[1_c].elements[0_c],
-            expr.elements[1_c].elements[0_c]
-        );
-    }
-#else
-    auto eval_expression_as (
-        decltype(term<number>{{0.0}} * number{} + number{}) const & expr,
-        boost::hana::basic_type<number>,
-        boost::hana::tuple<>)
-    {
-        std::cout << "User naxpy!  ";
-        return naxpy(
-            expr.left().left().value(),
-            expr.left().right().value(),
-            expr.right().value()
-        );
-    }
-#endif
-
-}
-
-void user_expression_transform ()
-{
-    std::cout << "\nuser_expression_transform()\n";
-
-    term<user_2::number> a{{1.0}};
-    term<user_2::number> x{{42.0}};
-    term<user_2::number> y{{3.0}};
-
-    bp17::expression<
-        bp17::expr_kind::plus,
-        bp17::expression<
-            bp17::expr_kind::multiplies,
-            term<user_2::number>,
-            term<user_2::number>
-        >,
-        term<user_2::number>
-    > expr = a * x + y;
-
-    // TODO: This was an error (user:: vs. user_2::).  Document for users that
-    // they should catch an expression in an auto var to diagnose these sorts
-    // of things.
-#if 0
-    bp17::expression<
-        bp17::expr_kind::multiplies,
-        term<user::number>,
-        term<user::number>
-    > expr = a * x;
-#endif
-
-    user_2::number result = expr;
-
-    std::cout << "expr=" << result.value << "\n"; // 45
-
-    std::cout << "\n";
-}
-
 int main ()
 {
     term_plus_x();
@@ -1257,5 +1173,4 @@ int main ()
     default_eval();
     user_eval_expression_as();
     user_operator_eval();
-    user_expression_transform();
 }
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 4a0c7a7..ab1fbf0 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -16,6 +16,7 @@ macro(add_test_executable name)
 endmacro()
 
 add_test_executable(print)
+add_test_executable(user_expression_transform)
 add_test_executable(placeholder_eval)
 add_test_executable(call_expr)
 add_test_executable(reference_returns)
diff --git a/test/user_expression_transform.cpp b/test/user_expression_transform.cpp
new file mode 100644
index 0000000..806fdb4
--- /dev/null
+++ b/test/user_expression_transform.cpp
@@ -0,0 +1,92 @@
+#define BOOST_PROTO17_CONVERSION_OPERATOR_TEMPLATE
+#include "expression.hpp"
+
+#include <gtest/gtest.h>
+
+#include <sstream>
+
+
+template <typename T>
+using term = boost::proto17::terminal<T>;
+
+namespace bp17 = boost::proto17;
+
+
+namespace user_2 {
+
+    struct number
+    {
+        double value;
+    };
+
+    number naxpy (number a, number x, number y)
+    { return number{a.value * x.value + y.value}; }
+
+#if 0
+    auto eval_expression_as (
+        bp17::expression<
+            bp17::expr_kind::plus,
+            bp17::expression<
+                bp17::expr_kind::multiplies,
+                term<number>,
+                term<number>
+            >,
+            term<number>
+        > const & expr,
+        boost::hana::basic_type<number>)
+    {
+        std::cout << "User naxpy!  ";
+        using namespace boost::hana::literals;
+        return naxpy(
+            expr.elements[0_c].elements[0_c].elements[0_c],
+            expr.elements[0_c].elements[1_c].elements[0_c],
+            expr.elements[1_c].elements[0_c]
+        );
+    }
+#else
+    auto eval_expression_as (
+        decltype(term<number>{{0.0}} * number{} + number{}) const & expr,
+        boost::hana::basic_type<number>,
+        boost::hana::tuple<>)
+    {
+        std::cout << "User naxpy!  ";
+        return naxpy(
+            expr.left().left().value(),
+            expr.left().right().value(),
+            expr.right().value()
+        );
+    }
+#endif
+
+}
+
+TEST(user_expression_transform, test_user_expression_transform)
+{
+    term<user_2::number> a{{1.0}};
+    term<user_2::number> x{{42.0}};
+    term<user_2::number> y{{3.0}};
+
+    bp17::expression<
+        bp17::expr_kind::plus,
+        bp17::expression<
+            bp17::expr_kind::multiplies,
+            term<user_2::number>,
+            term<user_2::number>
+        >,
+        term<user_2::number>
+    > expr = a * x + y;
+
+    // TODO: This was an error (user:: vs. user_2::).  Document for users that
+    // they should catch an expression in an auto var to diagnose these sorts
+    // of things.
+#if 0
+    bp17::expression<
+        bp17::expr_kind::multiplies,
+        term<user::number>,
+        term<user::number>
+    > expr = a * x;
+#endif
+
+    user_2::number result = expr;
+    EXPECT_EQ(result.value, 45);
+}