exp test added

test/test.cpp

@@ -44,3 +44,9 @@ TEST_CASE( "Basic power test", "[calc]") {
   REQUIRE( evaluate("43^") == 64 );
   REQUIRE( evaluate("25^") == 32 );
 }
+
+TEST_CASE( "Basic exp test", "[calc]") {
+  REQUIRE( evaluate("1exp") == 2.72 );
+  REQUIRE( evaluate("5exp") == 13.59 );
+  REQUIRE( evaluate("9exp") == 24.46 );
+}