Add comprehensive TDD infrastructure with 45 tests

- Add lib crate exposing modules for integration testing
- Add dev-dependencies: tokio-test 0.4, tempfile
- Refactor parse_csv_fields() as pure function for unit testing
- Add field validation (minimum 16 fields required)
- Fix repository last_insert_id using SELECT LAST_INSERT_ID()
- Add 10 lib tests for CSV parsing and date formatting
- Add 10 config tests for environment configuration
- Add 7 import tests for CSV file parsing
- Add 6 models tests for database structs
- Add 12 repository tests for CRUD operations

tests/config_test.rs

@@ -0,0 +1,105 @@
+//! Tests for the config module.
+//!
+//! AI AGENT NOTE: These tests verify configuration loading, environment
+//! parsing, and database connection URL generation.
+
+use invoice_generator::config::{Config, DatabaseConfig, Env};
+
+/// Tests that Env::default() returns Prod.
+#[test]
+fn env_default_is_prod() {
+    assert_eq!(Env::default(), Env::Prod);
+}
+
+/// Tests Env::from_str with valid short forms.
+#[test]
+fn env_from_str_valid_short() {
+    assert_eq!("prod".parse::<Env>().unwrap(), Env::Prod);
+    assert_eq!("dev".parse::<Env>().unwrap(), Env::Dev);
+    assert_eq!("test".parse::<Env>().unwrap(), Env::Test);
+}
+
+/// Tests Env::from_str with valid long forms (aliases).
+#[test]
+fn env_from_str_valid_aliases() {
+    assert_eq!("production".parse::<Env>().unwrap(), Env::Prod);
+    assert_eq!("development".parse::<Env>().unwrap(), Env::Dev);
+    assert_eq!("testing".parse::<Env>().unwrap(), Env::Test);
+}
+
+/// Tests Env::from_str is case-insensitive.
+#[test]
+fn env_from_str_case_insensitive() {
+    assert_eq!("PROD".parse::<Env>().unwrap(), Env::Prod);
+    assert_eq!("Dev".parse::<Env>().unwrap(), Env::Dev);
+    assert_eq!("TEST".parse::<Env>().unwrap(), Env::Test);
+}
+
+/// Tests Env::from_str with invalid value returns error.
+#[test]
+fn env_from_str_invalid() {
+    let result: Result<Env, _> = "invalid".parse();
+    assert!(result.is_err());
+    assert!(result.unwrap_err().contains("Unknown environment"));
+}
+
+/// Tests Env::as_str returns correct string.
+#[test]
+fn env_as_str() {
+    assert_eq!(Env::Prod.as_str(), "prod");
+    assert_eq!(Env::Dev.as_str(), "dev");
+    assert_eq!(Env::Test.as_str(), "test");
+}
+
+/// Tests Env::database_name returns correct database names.
+#[test]
+fn env_database_name() {
+    assert_eq!(Env::Prod.database_name(), "rusty_petroleum");
+    assert_eq!(Env::Dev.database_name(), "rusty_petroleum_dev");
+    assert_eq!(Env::Test.database_name(), "rusty_petroleum_test");
+}
+
+/// Tests DatabaseConfig::connection_url without password.
+#[test]
+fn db_connection_url_without_password() {
+    let config = DatabaseConfig {
+        host: "localhost".to_string(),
+        port: 3306,
+        user: "test_user".to_string(),
+        password: "".to_string(),
+        name: "test_db".to_string(),
+    };
+
+    let url = config.connection_url();
+    assert_eq!(url, "mysql://test_user@localhost:3306/test_db");
+}
+
+/// Tests DatabaseConfig::connection_url with password.
+#[test]
+fn db_connection_url_with_password() {
+    let config = DatabaseConfig {
+        host: "localhost".to_string(),
+        port: 3306,
+        user: "test_user".to_string(),
+        password: "secret".to_string(),
+        name: "test_db".to_string(),
+    };
+
+    let url = config.connection_url();
+    assert_eq!(url, "mysql://test_user:secret@localhost:3306/test_db");
+}
+
+/// Tests DatabaseConfig::connection_url with custom port.
+#[test]
+fn db_connection_url_custom_port() {
+    let config = DatabaseConfig {
+        host: "127.0.0.1".to_string(),
+        port: 3307,
+        user: "user".to_string(),
+        password: "pass".to_string(),
+        name: "mydb".to_string(),
+    };
+
+    let url = config.connection_url();
+    assert_eq!(url, "mysql://user:pass@127.0.0.1:3307/mydb");
+}