Implemented phase 3 for the POC prototype in the Website service.

Services/Website/Tests/App/AppTests.swift

@@ -127,6 +127,52 @@ struct AppTests {
         }
     }
 
+    @Test
+    func `buying to open a sale record for its buyer alone`() async throws {
+        try await app(
+            staticFilesPath: staticFilesPath
+        ).test(.router) { client in
+            let form: HTTPFields = [.contentType: "application/x-www-form-urlencoded"]
+            let cookie = try await client.execute(
+                uri: "/sign-in",
+                method: .post,
+                headers: form,
+                body: ByteBuffer(string: "return=/")
+            ) { response in
+                String(try #require(response.headers[.setCookie]).prefix { $0 != ";" })
+            }
+            var signedIn = form
+
+            signedIn[.cookie] = cookie
+
+            let sale = try await client.execute(
+                uri: "/listing/echo-country-3/buy",
+                method: .post,
+                headers: signedIn
+            ) { response in
+                #expect(response.status == .seeOther)
+
+                return try #require(response.headers[.location])
+            }
+
+            try await client.execute(
+                uri: sale,
+                method: .get,
+                headers: [.cookie: cookie]
+            ) { response in
+                #expect(response.status == .ok)
+                #expect(String(buffer: response.body).contains("Awaiting payment"))
+            }
+
+            try await client.execute(
+                uri: sale,
+                method: .get
+            ) { response in
+                #expect(response.status == .found)
+            }
+        }
+    }
+
     @Test
     func `error page to be served for an unknown listing`() async throws {
         try await app(