add cases for sqrt test

test/test.cpp

@@ -36,4 +36,6 @@ TEST_CASE( "Test modulo function", "[calc]") {
 
 TEST_CASE("Test sqrt function", "[calc]") {
   REQUIRE( evaluate("9sqrt") == 3 );
+  REQUIRE( evaluate("49sqrt") == 7 );
+  REQUIRE( evaluate("0sqrt") == 0 );
 }