Move more test code to standalone tests.

test/user_operator_eval.cpp

@@ -0,0 +1,78 @@
+#define BOOST_PROTO17_CONVERSION_OPERATOR_TEMPLATE
+#include "expression.hpp"
+
+#include <gtest/gtest.h>
+
+
+template <typename T>
+using term = boost::proto17::terminal<T>;
+
+namespace bp17 = boost::proto17;
+
+
+namespace user {
+
+    struct number
+    {
+        explicit operator double () const { return value; }
+
+        double value;
+    };
+
+    // User-defined binary-plus!  With weird semantics!
+    template <typename A, typename B>
+    inline auto eval_plus (A a, B b)
+    { return number{a.value - b.value}; }
+
+}
+
+TEST(user_operator_eval, test_user_operator_eval)
+{
+    term<user::number> unity{{1.0}};
+    double d_ = 42.0;
+    term<user::number> i{{d_}};
+    bp17::expression<
+        bp17::expr_kind::plus,
+        term<user::number>,
+        term<user::number>
+    > expr = unity + std::move(i);
+    bp17::expression<
+        bp17::expr_kind::plus,
+        term<user::number>,
+        bp17::expression<
+            bp17::expr_kind::plus,
+            term<user::number>,
+            term<user::number>
+        >
+    > unevaluated_expr = unity + std::move(expr);
+
+    {
+        double result = unity;
+        EXPECT_EQ(result, 1);
+    }
+
+    {
+        double result = expr;
+        EXPECT_EQ(result, -41);
+    }
+
+    {
+        double result = unevaluated_expr;
+        EXPECT_EQ(result, 42);
+    }
+
+    {
+        double result = (double)evaluate(unity, 5, 6, 7);
+        EXPECT_EQ(result, 1);
+    }
+
+    {
+        double result = (double)evaluate(expr);
+        EXPECT_EQ(result, -41);
+    }
+
+    {
+        double result = (double)evaluate(unevaluated_expr, std::string("15"));
+        EXPECT_EQ(result, 42);
+    }
+}