TEST: Ported integration_tests/enum_02.py from LPython

integration_tests/enum_02.cpp

@@ -0,0 +1,47 @@
+#include <iostream>
+
+enum MolecularMass {
+    water = 18,
+    methane = 16,
+    ammonia = 17,
+    oxygen = 16
+};
+
+enum RelativeCharge {
+    proton = 1,
+    electron = -1,
+    neutron = 0
+};
+
+void test_mm() {
+    std::cout << methane << " " << oxygen << std::endl;
+    if( methane != oxygen ) {
+        exit(2);
+    }
+
+    std::cout << ammonia - methane << std::endl;
+    if( ammonia - methane != 1 ) {
+        exit(2);
+    }
+
+    std::cout << water << " " << oxygen + 2 << std::endl;
+    if( water != oxygen + 2 ) {
+        exit(2);
+    }
+}
+
+void test_rc() {
+    std::cout << proton << " " << electron << " " << neutron << std::endl;
+    if( proton + electron != neutron ) {
+        exit(2);
+    }
+}
+
+int main() {
+
+test_mm();
+test_rc();
+
+return 0;
+
+}