Added unit tests

tests/providers/mod_tests.rs

@@ -0,0 +1,36 @@
+use gman::providers::{ParseProviderError, SupportedProvider};
+use gman::providers::local::LocalProvider;
+use std::str::FromStr;
+
+#[test]
+fn test_supported_provider_from_str_valid() {
+    assert_eq!(
+        SupportedProvider::from_str("local").unwrap(),
+        SupportedProvider::Local(LocalProvider)
+    );
+    assert_eq!(
+        SupportedProvider::from_str("LOCAL").unwrap(),
+        SupportedProvider::Local(LocalProvider)
+    );
+}
+
+#[test]
+fn test_supported_provider_from_str_invalid() {
+    let err = SupportedProvider::from_str("invalid").unwrap_err();
+    assert_eq!(
+        err.to_string(),
+        "unsupported provider 'invalid'"
+    );
+}
+
+#[test]
+fn test_supported_provider_display() {
+    let provider = SupportedProvider::Local(LocalProvider);
+    assert_eq!(provider.to_string(), "local");
+}
+
+#[test]
+fn test_parse_provider_error_display() {
+    let err = ParseProviderError::Unsupported("test".to_string());
+    assert_eq!(err.to_string(), "unsupported provider 'test'");
+}