feat: Adding documentation comments.

Tests/ConfigurationClientTests/ConfigurationClientTests.swift

@@ -141,6 +141,27 @@ struct ConfigurationClientTests: TestCase {
       }
     }
   }
+
+  @Test
+  func writeCreatesBackupFile() async throws {
+    try await withDependencies {
+      $0.fileClient = .liveValue
+    } operation: {
+      let client = ConfigurationClient.liveValue
+
+      try await withGeneratedConfigFile(named: "config.toml", client: client) { configFile in
+        @Dependency(\.fileClient) var fileClient
+
+        let backupUrl = configFile.url.appendingPathExtension(".back")
+        #expect(fileClient.fileExists(backupUrl) == false)
+
+        let config = Configuration()
+        try await client.write(config, to: configFile)
+
+        #expect(fileClient.fileExists(backupUrl))
+      }
+    }
+  }
 }
 
 func generateFindEnvironments(file: File) -> [[String: String]] {