diff --git a/Cargo.lock b/Cargo.lock
index 2676bf42..d9b9276d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -329,6 +329,16 @@ version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "877a4ace8713b0bcf2a4e7eec82529c029f1d0619886d18145fea96c3ffe5c0f"
 
+[[package]]
+name = "errno"
+version = "0.3.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "778e2ac28f6c47af28e4907f13ffd1e1ddbd400980a9abd7c8df189bf578a5ad"
+dependencies = [
+ "libc",
+ "windows-sys",
+]
+
 [[package]]
 name = "fallible-iterator"
 version = "0.3.0"
@@ -341,6 +351,12 @@ version = "0.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7360491ce676a36bf9bb3c56c1aa791658183a54d2744120f27285738d90465a"
 
+[[package]]
+name = "fastrand"
+version = "2.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "37909eebbb50d72f9059c3b6d82c0463f2ff062c9e95845c43a6c9c0355411be"
+
 [[package]]
 name = "foldhash"
 version = "0.1.5"
@@ -517,6 +533,12 @@ dependencies = [
  "vcpkg",
 ]
 
+[[package]]
+name = "linux-raw-sys"
+version = "0.9.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cd945864f07fe9f5371a27ad7b52a172b4b499999f1d97574c9fa68373937e12"
+
 [[package]]
 name = "lock_api"
 version = "0.4.13"
@@ -603,6 +625,7 @@ dependencies = [
  "rayon",
  "rusqlite",
  "serde",
+ "tempfile",
  "thiserror",
  "toml",
  "tracing",
@@ -867,6 +890,19 @@ dependencies = [
  "smallvec",
 ]
 
+[[package]]
+name = "rustix"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c71e83d6afe7ff64890ec6b71d6a69bb8a610ab78ce364b3352876bb4c801266"
+dependencies = [
+ "bitflags",
+ "errno",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys",
+]
+
 [[package]]
 name = "rustversion"
 version = "1.0.21"
@@ -989,6 +1025,19 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "tempfile"
+version = "3.20.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e8a64e3985349f2441a1a9ef0b853f869006c3855f2cda6862a94d26ebb9d6a1"
+dependencies = [
+ "fastrand",
+ "getrandom 0.3.3",
+ "once_cell",
+ "rustix",
+ "windows-sys",
+]
+
 [[package]]
 name = "thiserror"
 version = "2.0.12"
diff --git a/Cargo.toml b/Cargo.toml
index 5574ae83..4bcb495b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,6 +3,9 @@ name = "nyx"
 version = "0.1.0"
 edition = "2024"
 
+[dev-dependencies]
+tempfile = "3"
+
 [dependencies]
 directories = "6.0.0"
 clap = { version = "4.5.40", features = ["derive"] }
diff --git a/src/utils/config.rs b/src/utils/config.rs
index dfb28cf4..a72f4548 100644
--- a/src/utils/config.rs
+++ b/src/utils/config.rs
@@ -282,3 +282,42 @@ fn merge_configs(mut default: Config, user: Config) -> Config {
 
     default
 }
+
+#[test]
+fn merge_configs_dedupes_and_keeps_order() {
+  let mut default_cfg = Config::default();
+  default_cfg.scanner.excluded_extensions = vec!["rs".into(), "toml".into()];
+
+  let mut user_cfg = Config::default();
+  user_cfg.scanner.excluded_extensions = vec!["jpg".into(), "rs".into()];
+
+  let merged = merge_configs(default_cfg, user_cfg);
+  
+  assert_eq!(merged.scanner.excluded_extensions, vec!["jpg", "rs", "toml"]);
+}
+
+#[test]
+fn load_creates_example_and_reads_user_overrides() {
+  let cfg_dir = tempfile::tempdir().unwrap();
+  let cfg_path = cfg_dir.path();
+  
+  let user_toml = r#"
+        [scanner]
+        one_file_system = true
+        excluded_extensions = ["foo"]
+
+        [output]
+        quiet = true
+    "#;
+  fs::write(cfg_path.join("nyx.local"), user_toml).unwrap();
+
+  let cfg = Config::load(cfg_path).expect("Config::load should succeed");
+
+  assert!(cfg_path.join("nyx.conf").is_file());
+  
+  assert!(cfg.scanner.one_file_system);
+  assert!(cfg.output.quiet);
+  assert!(cfg.scanner.excluded_extensions.contains(&"foo".to_string()));
+
+  assert!(!cfg.scanner.follow_symlinks);
+}
diff --git a/src/utils/ext.rs b/src/utils/ext.rs
index 21cee881..11fe5e0d 100644
--- a/src/utils/ext.rs
+++ b/src/utils/ext.rs
@@ -12,3 +12,19 @@ pub fn lowercase_ext(path: &std::path::Path) -> Option<&'static str> {
         _ => None,
     })
 }
+
+#[test]
+fn lowercase_ext_recognises_known_extensions() {
+  let cases = [
+    ("file.rs",  Some("rs")),
+    ("FILE.RS",  Some("rs")),
+    ("main.cpp", Some("cpp")),
+    ("script.PY",Some("py")),
+    ("index.tsx",Some("ts")),
+    ("style.css",None),      // unsupported
+  ];
+
+  for (file, expected) in cases {
+    assert_eq!(lowercase_ext(std::path::Path::new(file)), expected, "case: {file}");
+  }
+}
diff --git a/src/utils/mod.rs b/src/utils/mod.rs
index b4d2301b..826c3e9c 100644
--- a/src/utils/mod.rs
+++ b/src/utils/mod.rs
@@ -4,5 +4,4 @@ pub mod project;
 pub(crate) mod query_cache;
 
 pub use config::Config;
-// Re-export commonly used functions for convenience
 pub use project::get_project_info;
diff --git a/src/utils/project.rs b/src/utils/project.rs
index 50024f4e..5bc10074 100644
--- a/src/utils/project.rs
+++ b/src/utils/project.rs
@@ -28,3 +28,36 @@ pub fn sanitize_project_name(name: &str) -> String {
         .collect::<Vec<_>>()
         .join("_")
 }
+
+#[test]
+fn sanitize_project_name_is_idempotent_and_lossless_enough() {
+  let samples = [
+    ("My Project",      "my_project"),
+    ("Hello-World",     "hello-world"),
+    ("mixed_case",      "mixed_case"),
+    ("tabs\tspaces\n",  "tabs_spaces"),
+    ("   multiple   ",  "multiple"),
+    ("weird@$*chars",   "weird_chars"),
+  ];
+
+  for (input, expected) in samples {
+    assert_eq!(sanitize_project_name(input), expected, "input: {}", input);
+    assert_eq!(sanitize_project_name(expected), expected);
+  }
+}
+
+#[test]
+fn get_project_info_uses_sanitized_name_in_sqlite_path() {
+  let tmp = tempfile::tempdir().unwrap();
+  let root = tmp.path();
+  
+  let project_dir = root.join("Example Project");
+  std::fs::create_dir(&project_dir).unwrap();
+
+  let (project_name, db_path) =
+    get_project_info(&project_dir, root).expect("should detect project");
+
+  assert_eq!(project_name, "Example Project");
+  assert_eq!(db_path, root.join("example_project.sqlite"));
+}
+