test: improve email client unit test

Cargo.toml

@@ -67,3 +67,4 @@ quickcheck = "1.0.3"
 quickcheck_macros = "1.0.0"
 rand = "0.8.5"
 wiremock = "0.6.0"
+serde_json = "1"

src/email_client.rs

@@ -40,7 +40,7 @@ impl EmailClient {
             html_body: html_content.to_owned(),
             text_body: text_content.to_owned(),
         };
-        let builder = self
+        let _builder = self
             .http_client
             .post(&url)
             .header(
@@ -54,6 +54,7 @@ impl EmailClient {
     }
 }
 #[derive(serde::Serialize)]
+#[serde(rename_all = "PascalCase")]
 struct SendEmailRequest {
     from: String,
     to: String,
@@ -71,17 +72,43 @@ mod tests {
     use fake::faker::lorem::en::{Paragraph, Sentence};
     use fake::{Fake, Faker};
     use secrecy::Secret;
-    use wiremock::matchers::any;
-    use wiremock::{Mock, MockServer, ResponseTemplate};
+    use wiremock::matchers::{header, header_exists, method, path};
+    use wiremock::{Mock, MockServer, Request, ResponseTemplate};
+
+    struct SendEmailBodyMatcher;
+
+    impl wiremock::Match for SendEmailBodyMatcher {
+        fn matches(&self, request: &Request) -> bool {
+            // Try to parse the body as a JSON value
+            let result: Result<serde_json::Value, _> = serde_json::from_slice(&request.body);
+            if let Ok(body) = result {
+                dbg!(&body);
+                // Check that all the mandatory fields are populated
+                // without inspecting the field values
+                body.get("From").is_some()
+                    && body.get("To").is_some()
+                    && body.get("Subject").is_some()
+                    && body.get("HtmlBody").is_some()
+                    && body.get("TextBody").is_some()
+            } else {
+                // If parsing failed, do not match the request
+                false
+            }
+        }
+    }
 
     #[tokio::test]
-    async fn send_email_fires_a_request_to_base_url() {
+    async fn send_email_sends_the_expected_request() {
         // Arrange
         let mock_server = MockServer::start().await;
         let sender = SubscriberEmail::parse(SafeEmail().fake()).unwrap();
         let email_client = EmailClient::new(mock_server.uri(), sender, Secret::new(Faker.fake()));
 
-        Mock::given(any())
+        Mock::given(header_exists("X-Postmark-Server-Token"))
+            .and(header("Content-Type", "application/json"))
+            .and(path("/email"))
+            .and(method("POST"))
+            .and(SendEmailBodyMatcher)
             .respond_with(ResponseTemplate::new(200))
             .expect(1)
             .mount(&mock_server)
@@ -97,5 +124,6 @@ mod tests {
             .await;
 
         // Assert
+        // Mock expectations are checked on drop
     }
 }

src/routes/subscriptions.rs

@@ -1,6 +1,5 @@
 use crate::domain::SubscriberEmail;
 use crate::domain::{NewSubscriber, SubscriberName};
-use crate::email_client;
 use crate::startup::AppState;
 use axum::extract::State;
 use axum::routing::post;