feat: Adding Test visibility (#113)

* feat: try to panic by calling private fn

* feat: removing panic test

* nit: format

* nit

listings/ch00-getting-started/visibility/src/tests.cairo

@@ -1,2 +1,26 @@
-mod tests { // TODO
+mod tests {
+    use visibility::{visibility::{IExampleContract, ExampleContract}};
+
+    use starknet::{
+        ContractAddress, get_contract_address, contract_address_const, call_contract_syscall,
+        testing::{set_contract_address}
+    };
+
+    fn setup() -> ExampleContract::ContractState {
+        let mut state = ExampleContract::contract_state_for_testing();
+        let contract_address = contract_address_const::<0x1>();
+        set_contract_address(contract_address);
+        state
+    }
+
+    #[test]
+    #[available_gas(2000000000)]
+    fn can_call_set_and_get() {
+        let mut state = setup();
+        let init_value: u32 = 42;
+        state.set(init_value);
+        let received_value = state.get();
+
+        assert(received_value == init_value, 'wrong value received');
+    }
 }