Utility functions for tests

We have a few code paths that some url paths can run when we receive invalid input. We'll write one new test: `handler_handles_empty_pokemon` .

The new test, in addition to the one we've already written needs an `ApiGatewayProxyRequest` which is quite large to write out each time. Inside of the `tests` sub-module we can add a helper function to construct and return a new `ApiGatewayProxyRequest`.

The `fake_request` function will accept a `path` that we use in the `path: Some(path)` field of the `ApiGatewayProxyRequest`.

```rust
fn fake_request(
    path: String,
) -> ApiGatewayProxyRequest {
    ApiGatewayProxyRequest {
        resource: None,
        path: Some(path),
        http_method: Method::GET,
        headers: HeaderMap::new(),
        multi_value_headers: HeaderMap::new(),
        query_string_parameters: HashMap::new(),
        multi_value_query_string_parameters:
            HashMap::new(),
        path_parameters: HashMap::new(),
        stage_variables: HashMap::new(),
        request_context:
            ApiGatewayProxyRequestContext {
                account_id: None,
                resource_id: None,
                operation_name: None,
                stage: None,
                domain_name: None,
                domain_prefix: None,
                request_id: None,
                protocol: None,
                identity: ApiGatewayRequestIdentity {
                    cognito_identity_pool_id: None,
                    account_id: None,
                    cognito_identity_id: None,
                    caller: None,
                    api_key: None,
                    api_key_id: None,
                    access_key: None,
                    source_ip: None,
                    cognito_authentication_type: None,
                    cognito_authentication_provider:
                        None,
                    user_arn: None,
                    user_agent: None,
                    user: None,
                },
                resource_path: None,
                authorizer: HashMap::new(),
                http_method: Method::GET,
                request_time: None,
                request_time_epoch: 0,
                apiid: None,
            },
        body: None,
        is_base64_encoded: Some(false),
    }
}
```

and we can use it in the `handler_handles` test.

```rust
async fn handler_handles() {
    let event = fake_request(
        "/api/pokemon/bulbasaur".to_string(),
    );

    assert_eq!(
        handler(event.clone(), Context::default())
            .await
            .unwrap(),
        ApiGatewayProxyResponse {
            status_code: 200,
            headers: HeaderMap::new(),
            multi_value_headers: HeaderMap::new(),
            body: Some(Body::Text(
                serde_json::to_string(&PokemonHp {
                    name: String::from("Bulbasaur"),
                    hp: 45
                },)
                .unwrap()
            )),
            is_base64_encoded: Some(false),
        }
    )
}
```

Our new test will panic because of the `todo` macro, so we can use the `should_panic` attribute macro to test against the expected panic message.

The test will exercise the `400` codepath, which happens when the path doesn't include a Pokemon name. We could return an empty response as if we hadn't found a Pokemon, but it's most likely that an empty path segment is a client mistake, having passed in an empty string or misconstructed the path.

```rust
async fn handler_handles_empty_pokemon() {
    let event =
        fake_request("/api/pokemon//".to_string());
    handler(event.clone(), Context::default())
        .await
        .unwrap();
}
```

All tests should pass at this point

crates/pokemon-api/src/main.rs

@@ -78,11 +78,46 @@ mod tests {
 
     #[tokio::test]
     async fn handler_handles() {
-        let event = ApiGatewayProxyRequest {
+        let event = fake_request(
+            "/api/pokemon/bulbasaur".to_string(),
+        );
+
+        assert_eq!(
+            handler(event.clone(), Context::default())
+                .await
+                .unwrap(),
+            ApiGatewayProxyResponse {
+                status_code: 200,
+                headers: HeaderMap::new(),
+                multi_value_headers: HeaderMap::new(),
+                body: Some(Body::Text(
+                    serde_json::to_string(&PokemonHp {
+                        name: String::from("Bulbasaur"),
+                        hp: 45
+                    },)
+                    .unwrap()
+                )),
+                is_base64_encoded: Some(false),
+            }
+        )
+    }
+
+    #[tokio::test]
+    #[should_panic(expected = "not yet implemented")]
+    async fn handler_handles_empty_pokemon() {
+        let event =
+            fake_request("/api/pokemon//".to_string());
+        handler(event.clone(), Context::default())
+            .await
+            .unwrap();
+    }
+
+    fn fake_request(
+        path: String,
+    ) -> ApiGatewayProxyRequest {
+        ApiGatewayProxyRequest {
             resource: None,
-            path: Some(
-                "/api/pokemon/bulbasaur".to_string(),
-            ),
+            path: Some(path),
             http_method: Method::GET,
             headers: HeaderMap::new(),
             multi_value_headers: HeaderMap::new(),
@@ -126,25 +161,6 @@ mod tests {
                 },
             body: None,
             is_base64_encoded: Some(false),
-        };
-
-        assert_eq!(
-            handler(event.clone(), Context::default())
-                .await
-                .unwrap(),
-            ApiGatewayProxyResponse {
-                status_code: 200,
-                headers: HeaderMap::new(),
-                multi_value_headers: HeaderMap::new(),
-                body: Some(Body::Text(
-                    serde_json::to_string(&PokemonHp {
-                        name: String::from("Bulbasaur"),
-                        hp: 45
-                    },)
-                    .unwrap()
-                )),
-                is_base64_encoded: Some(false),
-            }
-        )
+        }
     }
 }