Fix "Testing Smart Contracts" code (#2327)

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## Introduced changes

<!-- A brief description of the changes -->

- After testing this section some code snippets and explanations needed
to be updated

## Checklist

<!-- Make sure all of these are complete -->

- [x] Linked relevant issue
- [x] Updated relevant documentation
- [x] Added relevant tests
- [x] Performed self-review of the code
- [x] Added changes to `CHANGELOG.md`

docs/src/testing/contracts.md

@@ -1,6 +1,7 @@
 # Testing Smart Contracts
 
 > ℹ️ **Info**
+> 
 > To use the library functions designed for testing smart contracts,
 > you need to add `snforge_std` package as a dependency in
 > your [`Scarb.toml`](https://docs.swmansion.com/scarb/docs/guides/dependencies.html#development-dependencies)
@@ -15,11 +16,11 @@ writing smart contracts, you often want to test their interactions with the bloc
 
 ## The Test Contract
 
-In this tutorial we will be using this Starknet contract
+In this tutorial we will be using this Starknet contract, in a new `using_dispatchers` package.
 
 ```rust
 #[starknet::interface]
-trait IHelloStarknet<TContractState> {
+pub trait IHelloStarknet<TContractState> {
     fn increase_balance(ref self: TContractState, amount: felt252);
     fn get_balance(self: @TContractState) -> felt252;
 }
@@ -54,6 +55,7 @@ Let's write a test that will deploy the `HelloStarknet` contract and call some f
 
 ```rust
 use snforge_std::{ declare, ContractClassTrait };
+use using_dispatchers::{ IHelloStarknetDispatcher, IHelloStarknetDispatcherTrait };
 
 #[test]
 fn call_and_invoke() {
@@ -122,14 +124,12 @@ mod HelloStarknet {
 
         // Panics
         fn do_a_panic(self: @ContractState) {
-            let mut arr = ArrayTrait::new();
-            arr.append('PANIC');
-            arr.append('DAYTAH');
-            panic(arr);
+            panic(array!['PANIC', 'DAYTAH']);
         }
 
         fn do_a_string_panic(self: @ContractState) {
-            assert!(false, "This is panicking with a string, which can be longer than 31 characters");
+            // A macro which allows panicking with a ByteArray (string) instance
+            panic!("This is panicking with a string, which can be longer than 31 characters");
         }
     }
 }
@@ -139,11 +139,9 @@ If we called this function in a test, it would result in a failure.
 
 ```rust
 #[test]
-#[feature("safe_dispatcher")]
 fn failing() {
-    // ...
-
-    let (contract_address, _) = contract.deploy(@calldata).unwrap();
+    let contract = declare("HelloStarknet").unwrap();
+    let (contract_address, _) = contract.deploy(@array![]).unwrap();
     let dispatcher = IHelloStarknetDispatcher { contract_address };
 
     dispatcher.do_a_panic();
@@ -169,19 +167,25 @@ Failures:
 ### `SafeDispatcher`
 
 Using `SafeDispatcher` we can test that the function in fact panics with an expected message.
+Safe dispatcher is a special kind of dispatcher, which are not allowed in contracts themselves, 
+but are available for testing purposes.
+
+They allow using the contract without automatically unwrapping the result, which allows to catch the error like shown below.  
 
 ```rust
+// Add those to import safe dispatchers, which are autogenerated, like regular dispatchers
+use using_dispatchers::{ IHelloStarknetSafeDispatcher, IHelloStarknetSafeDispatcherTrait };
+
 #[test]
 #[feature("safe_dispatcher")]
 fn handling_errors() {
     // ...
-
+    let contract = declare("HelloStarknet").unwrap();
     let (contract_address, _) = contract.deploy(@calldata).unwrap();
     let safe_dispatcher = IHelloStarknetSafeDispatcher { contract_address };
 
-
     match safe_dispatcher.do_a_panic() {
-        Result::Ok(_) => panic_with_felt252('shouldve panicked'),
+        Result::Ok(_) => panic!("Entrypoint did not panic"),
         Result::Err(panic_data) => {
             assert(*panic_data.at(0) == 'PANIC', *panic_data.at(0));
             assert(*panic_data.at(1) == 'DAYTAH', *panic_data.at(1));
@@ -207,20 +211,20 @@ Similarly, you can handle the panics which use `ByteArray` as an argument (like
 // Necessary utility function import
 use snforge_std::byte_array::try_deserialize_bytearray_error;
 
-// ...
 #[test]
 #[feature("safe_dispatcher")]
 fn handling_string_errors() {
     // ...
-    let (contract_address, _) = contract.deploy(@calldata).unwrap();
+    let contract = declare("HelloStarknet").unwrap();
+    let (contract_address, _) = contract.deploy(@array![]).unwrap();
     let safe_dispatcher = IHelloStarknetSafeDispatcher { contract_address };
 
-    match safe_dispatcher.do_a_panic_with_bytearray() {
-        Result::Ok(_) => panic_with_felt252('shouldve panicked'),
+    match safe_dispatcher.do_a_string_panic() {
+        Result::Ok(_) => panic!("Entrypoint did not panic"),
         Result::Err(panic_data) => {
             let str_err = try_deserialize_bytearray_error(panic_data.span()).expect('wrong format');
             assert(
-                str_err == "This is a very long\n and multiline message that is certain to fill the buffer", 
+                str_err == "This is panicking with a string, which can be longer than 31 characters", 
                 'wrong string received'
             );
         }
@@ -231,7 +235,7 @@ You also could skip the de-serialization of the `panic_data`, and not use `try_d
 
 > 📝 **Note**
 > 
-> To operate with `SafeDispatcher` it's required to annotage its usage with `#[feature("safe_dispatcher")]`.
+> To operate with `SafeDispatcher` it's required to annotate its usage with `#[feature("safe_dispatcher")]`.
 > 
 > There are 3 options:
 > - module-level declaration