diff --git a/tests/absolutize_contracts.rs b/tests/absolutize_contracts.rs
new file mode 100644
index 0000000..b5c888a
--- /dev/null
+++ b/tests/absolutize_contracts.rs
@@ -0,0 +1,153 @@
+#![cfg(any(target_family = "unix", target_family = "windows"))]
+
+#[cfg(target_family = "windows")]
+use std::path::PathBuf;
+use std::{borrow::Cow, env, path::Path};
+
+use sugar_path::SugarPath;
+
+#[derive(Clone, Copy)]
+enum ExpectedCow {
+  Borrowed,
+  Owned,
+}
+
+fn assert_result(
+  result: Cow<'_, Path>,
+  input: &Path,
+  expected: &Path,
+  expected_cow: ExpectedCow,
+  context: &str,
+) {
+  assert_eq!(result.as_os_str(), expected.as_os_str(), "{context}");
+  match (expected_cow, result) {
+    (ExpectedCow::Borrowed, Cow::Borrowed(result)) => {
+      assert!(std::ptr::eq(result, input), "{context}: result did not borrow the receiver");
+    }
+    (ExpectedCow::Owned, Cow::Owned(_)) => {}
+    (ExpectedCow::Borrowed, Cow::Owned(_)) => panic!("{context}: expected borrowed result"),
+    (ExpectedCow::Owned, Cow::Borrowed(_)) => panic!("{context}: expected owned result"),
+  }
+}
+
+fn assert_ambient_case(input: &Path, expected: &Path, expected_cow: ExpectedCow, name: &str) {
+  assert_result(input.absolutize(), input, expected, expected_cow, &format!("{name} strict"));
+  assert_result(
+    input.try_absolutize().expect("fixture should resolve against cwd"),
+    input,
+    expected,
+    expected_cow,
+    &format!("{name} try"),
+  );
+}
+
+fn assert_string_receiver(input: String, expected: &Path) {
+  let strict = input.absolutize();
+  assert_eq!(strict.as_os_str(), expected.as_os_str());
+  assert!(matches!(strict, Cow::Owned(_)));
+
+  let fallible = input.try_absolutize().expect("String fixture should resolve against cwd");
+  assert_eq!(fallible.as_os_str(), expected.as_os_str());
+  assert!(matches!(fallible, Cow::Owned(_)));
+}
+
+#[cfg(target_family = "unix")]
+#[test]
+fn unix_ambient_absolutize_and_try_contract_matrix() {
+  let cwd = env::current_dir().expect("read current directory");
+
+  let clean = Path::new("/some/β/file");
+  assert_ambient_case(clean, clean, ExpectedCow::Borrowed, "clean absolute");
+  assert_ambient_case(
+    Path::new("/some/./β/../file/"),
+    Path::new("/some/file"),
+    ExpectedCow::Owned,
+    "dirty absolute",
+  );
+  assert_ambient_case(Path::new(""), &cwd, ExpectedCow::Owned, "empty");
+  assert_ambient_case(Path::new("."), &cwd, ExpectedCow::Owned, "dot");
+  assert_ambient_case(
+    Path::new("./pkg//β/../file/"),
+    &cwd.join("pkg/file"),
+    ExpectedCow::Owned,
+    "ordinary relative",
+  );
+
+  assert_string_receiver("./owned/../file".to_owned(), &cwd.join("file"));
+}
+
+#[cfg(target_family = "windows")]
+fn current_ordinary_disk_drive(path: &Path) -> Option<u8> {
+  use std::path::{Component, Prefix};
+
+  match path.components().next() {
+    Some(Component::Prefix(prefix)) => match prefix.kind() {
+      Prefix::Disk(drive) => Some(drive),
+      _ => None,
+    },
+    _ => None,
+  }
+}
+
+#[cfg(target_family = "windows")]
+fn preserve_drive_spelling(path: &Path, drive: u8) -> PathBuf {
+  use std::{
+    ffi::OsString,
+    os::windows::ffi::{OsStrExt, OsStringExt},
+  };
+
+  let mut wide: Vec<u16> = path.as_os_str().encode_wide().collect();
+  if wide.get(1) == Some(&(b':' as u16)) {
+    wide[0] = drive as u16;
+  } else if wide.get(5) == Some(&(b':' as u16))
+    && wide.get(..4) == Some(&[b'\\' as u16, b'\\' as u16, b'?' as u16, b'\\' as u16])
+  {
+    wide[4] = drive as u16;
+  } else {
+    panic!("expected disk path, found {path:?}");
+  }
+  PathBuf::from(OsString::from_wide(&wide))
+}
+
+#[cfg(target_family = "windows")]
+#[test]
+fn windows_ambient_absolutize_and_try_contract_matrix() {
+  let cwd = env::current_dir().expect("read current directory");
+
+  let clean = Path::new(r"c:\some\β\file");
+  assert_ambient_case(clean, clean, ExpectedCow::Borrowed, "clean absolute");
+  assert_ambient_case(
+    Path::new(r"c:/some/.\β\../file\"),
+    Path::new(r"c:\some\file"),
+    ExpectedCow::Owned,
+    "dirty absolute",
+  );
+  assert_ambient_case(Path::new(""), &cwd, ExpectedCow::Owned, "empty");
+  assert_ambient_case(Path::new("."), &cwd, ExpectedCow::Owned, "dot");
+  assert_ambient_case(
+    Path::new(r".\pkg\\β\..\file\"),
+    &cwd.join(r"pkg\file"),
+    ExpectedCow::Owned,
+    "ordinary relative",
+  );
+
+  let root_relative = Path::new(r"\pkg\.\β\..\file\");
+  let mut expected = cwd.clone();
+  expected.push(r"\pkg\file");
+  assert_ambient_case(root_relative, &expected, ExpectedCow::Owned, "root relative");
+
+  if let Some(drive) = current_ordinary_disk_drive(&cwd) {
+    let drive = drive.to_ascii_lowercase();
+    let drive_relative = format!("{}:folder\\.\\file\\", drive as char);
+    let mut expected = preserve_drive_spelling(&cwd, drive);
+    expected.push(r"folder\file");
+    assert_ambient_case(
+      Path::new(&drive_relative),
+      &expected,
+      ExpectedCow::Owned,
+      "drive relative",
+    );
+  }
+
+  assert_string_receiver(r".\owned\..\file".to_owned(), &cwd.join("file"));
+}
diff --git a/tests/absolutize_invalid_encoding.rs b/tests/absolutize_invalid_encoding.rs
new file mode 100644
index 0000000..51e6921
--- /dev/null
+++ b/tests/absolutize_invalid_encoding.rs
@@ -0,0 +1,137 @@
+#![cfg(any(target_family = "unix", target_family = "windows"))]
+
+use std::{borrow::Cow, path::Path};
+
+use sugar_path::SugarPath;
+
+#[cfg(target_family = "unix")]
+mod unix {
+  use std::{
+    env,
+    ffi::OsString,
+    os::unix::ffi::{OsStrExt, OsStringExt},
+    path::PathBuf,
+  };
+
+  use super::*;
+
+  fn path(bytes: &[u8]) -> PathBuf {
+    PathBuf::from(OsString::from_vec(bytes.to_vec()))
+  }
+
+  fn assert_bytes(actual: &Path, expected: &Path, context: &str) {
+    assert_eq!(actual.as_os_str().as_bytes(), expected.as_os_str().as_bytes(), "{context}",);
+  }
+
+  fn assert_ambient(input: &Path, expected: &Path, require_owned: bool, name: &str) {
+    let strict = input.absolutize();
+    assert_bytes(&strict, expected, &format!("{name} strict"));
+    if require_owned {
+      assert!(matches!(strict, Cow::Owned(_)), "{name} strict should own");
+    }
+
+    let fallible = input.try_absolutize().expect("fixture should resolve against cwd");
+    assert_bytes(&fallible, expected, &format!("{name} try"));
+    if require_owned {
+      assert!(matches!(fallible, Cow::Owned(_)), "{name} try should own");
+    }
+  }
+
+  #[test]
+  fn ambient_absolutization_preserves_invalid_unix_bytes() {
+    let clean = path(b"/sugar-path/invalid-\x80/file");
+    assert_ambient(&clean, &clean, false, "clean absolute");
+
+    let dirty = path(b"/sugar-path/invalid-\x80/./file/");
+    let normalized = path(b"/sugar-path/invalid-\x80/file");
+    assert_ambient(&dirty, &normalized, true, "dirty absolute");
+
+    let relative = path(b"pkg/invalid-\x80/./file/");
+    let expected =
+      env::current_dir().expect("read current directory").join(path(b"pkg/invalid-\x80/file"));
+    assert_ambient(&relative, &expected, true, "relative");
+  }
+}
+
+#[cfg(target_family = "windows")]
+mod windows {
+  use std::{
+    env,
+    ffi::OsString,
+    os::windows::ffi::{OsStrExt, OsStringExt},
+    path::PathBuf,
+  };
+
+  use super::*;
+
+  const INVALID_UNIT: u16 = 0xd800;
+
+  fn invalid_path(before: &str, after: &str) -> PathBuf {
+    let mut wide: Vec<u16> = before.encode_utf16().collect();
+    wide.push(INVALID_UNIT);
+    wide.extend(after.encode_utf16());
+    PathBuf::from(OsString::from_wide(&wide))
+  }
+
+  fn assert_wide(actual: &Path, expected: &Path, context: &str) {
+    assert_eq!(
+      actual.as_os_str().encode_wide().collect::<Vec<_>>(),
+      expected.as_os_str().encode_wide().collect::<Vec<_>>(),
+      "{context}",
+    );
+  }
+
+  fn current_ordinary_disk_drive(path: &Path) -> Option<u8> {
+    use std::path::{Component, Prefix};
+
+    match path.components().next() {
+      Some(Component::Prefix(prefix)) => match prefix.kind() {
+        Prefix::Disk(drive) => Some(drive),
+        _ => None,
+      },
+      _ => None,
+    }
+  }
+
+  fn assert_ambient(input: &Path, expected: &Path, require_owned: bool, name: &str) {
+    let strict = input.absolutize();
+    assert_wide(&strict, expected, &format!("{name} strict"));
+    if require_owned {
+      assert!(matches!(strict, Cow::Owned(_)), "{name} strict should own");
+    }
+
+    let fallible = input.try_absolutize().expect("fixture should resolve against cwd");
+    assert_wide(&fallible, expected, &format!("{name} try"));
+    if require_owned {
+      assert!(matches!(fallible, Cow::Owned(_)), "{name} try should own");
+    }
+  }
+
+  #[test]
+  fn ambient_absolutization_preserves_invalid_windows_units() {
+    let cwd = env::current_dir().expect("read current directory");
+
+    let clean = invalid_path(r"C:\sugar-path\invalid-", r"\file");
+    assert_ambient(&clean, &clean, false, "clean absolute");
+
+    let dirty = invalid_path(r"C:\sugar-path\invalid-", r"\.\file\");
+    let normalized = invalid_path(r"C:\sugar-path\invalid-", r"\file");
+    assert_ambient(&dirty, &normalized, true, "dirty absolute");
+
+    let relative = invalid_path(r"pkg\invalid-", r"\.\file\");
+    let expected = cwd.join(invalid_path(r"pkg\invalid-", r"\file"));
+    assert_ambient(&relative, &expected, true, "relative");
+
+    let root_relative = invalid_path(r"\pkg\invalid-", r"\.\file\");
+    let mut expected = cwd.clone();
+    expected.push(invalid_path(r"\pkg\invalid-", r"\file"));
+    assert_ambient(&root_relative, &expected, true, "root relative");
+
+    if let Some(drive) = current_ordinary_disk_drive(&cwd) {
+      let prefix = format!("{}:pkg\\invalid-", drive as char);
+      let drive_relative = invalid_path(&prefix, r"\.\file\");
+      let expected = cwd.join(invalid_path(r"pkg\invalid-", r"\file"));
+      assert_ambient(&drive_relative, &expected, false, "drive relative");
+    }
+  }
+}
diff --git a/tests/absolutize_windows_roots.rs b/tests/absolutize_windows_roots.rs
new file mode 100644
index 0000000..3a56cbb
--- /dev/null
+++ b/tests/absolutize_windows_roots.rs
@@ -0,0 +1,45 @@
+#![cfg(target_family = "windows")]
+
+use std::{
+  borrow::Cow,
+  path::{Path, PathBuf},
+};
+
+use sugar_path::SugarPath;
+
+fn assert_explicit_case(cwd: &str, input: &str, expected: &str, name: &str) {
+  assert!(Path::new(cwd).is_absolute(), "{name}: fixture cwd is not absolute");
+
+  let borrowed = Path::new(input).absolutize_with(Path::new(cwd));
+  assert_eq!(borrowed.as_os_str(), Path::new(expected).as_os_str(), "{name} borrowed cwd");
+  assert!(matches!(borrowed, Cow::Owned(_)), "{name} borrowed cwd should own");
+
+  let owned = Path::new(input).absolutize_with(PathBuf::from(cwd));
+  assert_eq!(owned.as_os_str(), Path::new(expected).as_os_str(), "{name} owned cwd");
+  assert!(matches!(owned, Cow::Owned(_)), "{name} owned cwd should own");
+}
+
+#[test]
+fn windows_root_relative_inputs_use_the_exact_explicit_prefix() {
+  let cases = [
+    ("disk", r"C:\workspace", r"\pkg\.\temp\..\β\file\", r"C:\pkg\β\file"),
+    ("disk root", r"C:\workspace", r"\", r"C:\"),
+    ("UNC", r"\\Server\Share\workspace", r"\pkg\..\file\", r"\\Server\Share\file"),
+    ("UNC root", r"\\Server\Share\workspace", r"\", r"\\Server\Share\"),
+    ("verbatim disk", r"\\?\c:\workspace", r"\pkg\..\file\", r"\\?\c:\file"),
+    ("verbatim disk root", r"\\?\c:\workspace", r"\", r"\\?\c:\"),
+    (
+      "verbatim UNC",
+      r"\\?\UNC\Server\Share\workspace",
+      r"\pkg\..\file\",
+      r"\\?\UNC\Server\Share\file",
+    ),
+    // A verbatim UNC prefix is already rooted and absolute without an explicit
+    // RootDir component, so resolution strips the optional trailing separator.
+    ("verbatim UNC root", r"\\?\UNC\Server\Share\workspace", r"\", r"\\?\UNC\Server\Share"),
+  ];
+
+  for (name, cwd, input, expected) in cases {
+    assert_explicit_case(cwd, input, expected, name);
+  }
+}
diff --git a/tests/absolutize_without_cwd.rs b/tests/absolutize_without_cwd.rs
index a468f5c..9e9f91d 100644
--- a/tests/absolutize_without_cwd.rs
+++ b/tests/absolutize_without_cwd.rs
@@ -22,13 +22,17 @@ fn absolute_paths_do_not_require_current_directory() {
     let clean_output = clean.absolutize();
     assert!(matches!(clean_output, Cow::Borrowed(_)));
     assert_eq!(clean_output.as_os_str(), clean.as_os_str());
-    assert!(clean.try_absolutize().is_ok());
+    let clean_try = clean.try_absolutize().expect("clean absolute path should succeed");
+    assert!(matches!(clean_try, Cow::Borrowed(_)));
+    assert_eq!(clean_try.as_os_str(), clean.as_os_str());
 
     let dirty = Path::new("/sugar-path/../file.js/");
     let dirty_output = dirty.absolutize();
     assert!(matches!(dirty_output, Cow::Owned(_)));
     assert_eq!(dirty_output.as_os_str(), Path::new("/file.js").as_os_str());
-    assert!(dirty.try_absolutize().is_ok());
+    let dirty_try = dirty.try_absolutize().expect("dirty absolute path should succeed");
+    assert!(matches!(dirty_try, Cow::Owned(_)));
+    assert_eq!(dirty_try.as_os_str(), Path::new("/file.js").as_os_str());
 
     assert!(Path::new("relative.js").try_absolutize().is_err());
     assert!(std::panic::catch_unwind(|| Path::new("relative.js").absolutize()).is_err());