diff --git a/tests/invalid_encoding.rs b/tests/invalid_encoding.rs
index 791c504..020d19e 100644
--- a/tests/invalid_encoding.rs
+++ b/tests/invalid_encoding.rs
@@ -86,13 +86,14 @@ mod unix {
   }
 
   #[test]
-  fn slash_conversion_reports_and_replaces_invalid_encoding() {
-    let input = path(b"dir/\x80/file");
+  fn non_utf8_slash_policies_preserve_non_normalized_spelling() {
+    let input = path(b"./dir//invalid-\x80/../tail/");
+    let expected = "./dir//invalid-\u{fffd}/../tail/";
 
     assert!(input.try_to_slash().is_none());
     assert!(std::panic::catch_unwind(|| input.to_slash()).is_err());
     let lossy = input.to_slash_lossy();
-    assert_eq!(lossy, "dir/\u{fffd}/file");
+    assert_eq!(lossy, expected);
     assert!(matches!(&lossy, Cow::Owned(_)));
   }
 
@@ -319,13 +320,19 @@ mod windows {
   }
 
   #[test]
-  fn slash_conversion_reports_and_replaces_invalid_encoding() {
-    let input = invalid_path(r"dir\", r"\file");
+  fn invalid_unicode_slash_policies_preserve_non_normalized_spelling() {
+    let input = invalid_path(r".\dir\\invalid-", r"\..\tail\");
+    let expected = "./dir//invalid-\u{fffd}/../tail/";
 
     assert!(input.try_to_slash().is_none());
     assert!(std::panic::catch_unwind(|| input.to_slash()).is_err());
     let lossy = input.to_slash_lossy();
-    assert_eq!(lossy, "dir/\u{fffd}/file");
+    assert_eq!(lossy, expected);
+    assert!(matches!(&lossy, Cow::Owned(_)));
+
+    let no_native_separator = invalid_path("invalid-", "/tail");
+    let lossy = no_native_separator.to_slash_lossy();
+    assert_eq!(lossy, "invalid-\u{fffd}/tail");
     assert!(matches!(&lossy, Cow::Owned(_)));
   }
 
diff --git a/tests/owned_api.rs b/tests/owned_api.rs
index f63cdd3..81f1a81 100644
--- a/tests/owned_api.rs
+++ b/tests/owned_api.rs
@@ -69,28 +69,42 @@ fn into_normalized_matches_borrowed_api_for_dirty_paths() {
 #[test]
 fn owned_slash_apis_reuse_valid_unicode_buffers() {
   #[cfg(target_family = "unix")]
-  let (input, expected) = (
-    "/workspace/rolldown/crates/rolldown/src/module_loader/module_task.rs",
-    "/workspace/rolldown/crates/rolldown/src/module_loader/module_task.rs",
-  );
+  let cases = [
+    (
+      "/workspace/rolldown/crates/rolldown/src/module_loader/module_task.rs",
+      "/workspace/rolldown/crates/rolldown/src/module_loader/module_task.rs",
+    ),
+    (r"/root/./β/../tail//literal\name//", r"/root/./β/../tail//literal\name//"),
+  ];
   #[cfg(target_family = "windows")]
-  let (input, expected) = (
-    r"C:\workspace\rolldown\crates\rolldown\src\module_loader\module_task.rs",
-    "C:/workspace/rolldown/crates/rolldown/src/module_loader/module_task.rs",
-  );
+  let cases = [
+    (
+      r"C:\workspace\rolldown\crates\rolldown\src\module_loader\module_task.rs",
+      "C:/workspace/rolldown/crates/rolldown/src/module_loader/module_task.rs",
+    ),
+    (r"\\server\share\.\β\..\tail\\foreign/name\\", "//server/share/./β/../tail//foreign/name//"),
+    ("//server/share/./β/../tail//foreign/name//", "//server/share/./β/../tail//foreign/name//"),
+  ];
 
-  let path = owned_path_with_capacity(input);
-  let identity = buffer_identity(&path);
-  let slash = path.into_slash();
+  for (input, expected) in cases {
+    let path = owned_path_with_capacity(input);
+    let identity = buffer_identity(&path);
+    let slash = path.into_slash();
+    assert_eq!(slash, expected, "strict: input {input:?}");
+    assert_eq!((slash.as_ptr(), slash.capacity()), identity, "strict: input {input:?}");
 
-  assert_eq!(slash, expected);
-  assert_eq!((slash.as_ptr(), slash.capacity()), identity);
+    let path = owned_path_with_capacity(input);
+    let identity = buffer_identity(&path);
+    let slash = path.try_into_slash().expect("the fixture is valid Unicode");
+    assert_eq!(slash, expected, "try: input {input:?}");
+    assert_eq!((slash.as_ptr(), slash.capacity()), identity, "try: input {input:?}");
 
-  let path = owned_path_with_capacity(input);
-  let identity = buffer_identity(&path);
-  let slash = path.try_into_slash().expect("the fixture is valid Unicode");
-  assert_eq!(slash, expected);
-  assert_eq!((slash.as_ptr(), slash.capacity()), identity);
+    let path = owned_path_with_capacity(input);
+    let identity = buffer_identity(&path);
+    let slash = path.into_slash_lossy();
+    assert_eq!(slash, expected, "lossy: input {input:?}");
+    assert_eq!((slash.as_ptr(), slash.capacity()), identity, "lossy: input {input:?}");
+  }
 }
 
 #[cfg(target_family = "unix")]
@@ -101,13 +115,20 @@ fn owned_apis_preserve_and_replace_invalid_unix_encoding() {
     os::unix::ffi::{OsStrExt, OsStringExt},
   };
 
-  let input = PathBuf::from(OsString::from_vec(b"dir/invalid-\x80/./file".to_vec()));
-  let normalized = input.clone().into_normalized();
+  let normalize_input = PathBuf::from(OsString::from_vec(b"dir/invalid-\x80/./file".to_vec()));
+  let normalized = normalize_input.into_normalized();
   assert_eq!(normalized.as_os_str().as_bytes(), b"dir/invalid-\x80/file");
+
+  let input = PathBuf::from(OsString::from_vec(b"./dir//invalid-\x80/../tail/".to_vec()));
+
+  let strict = input.clone();
+  assert!(std::panic::catch_unwind(move || strict.into_slash()).is_err());
+
+  let recoverable = input.clone();
   let returned =
-    input.clone().try_into_slash().expect_err("invalid Unix encoding must be returned unchanged");
+    recoverable.try_into_slash().expect_err("invalid Unix encoding must be returned unchanged");
   assert_eq!(returned.as_os_str().as_bytes(), input.as_os_str().as_bytes());
-  assert_eq!(input.into_slash_lossy(), "dir/invalid-\u{fffd}/./file");
+  assert_eq!(input.into_slash_lossy(), "./dir//invalid-\u{fffd}/../tail/");
 }
 
 #[cfg(target_family = "windows")]
@@ -118,22 +139,36 @@ fn owned_apis_preserve_and_replace_invalid_windows_encoding() {
     os::windows::ffi::{OsStrExt, OsStringExt},
   };
 
-  let mut input_wide: Vec<u16> = r"C:\workspace\invalid-".encode_utf16().collect();
-  input_wide.push(0xd800);
-  input_wide.extend(r"\.\file".encode_utf16());
-  let input = PathBuf::from(OsString::from_wide(&input_wide));
+  let mut normalize_input_wide: Vec<u16> = r"C:\workspace\invalid-".encode_utf16().collect();
+  normalize_input_wide.push(0xd800);
+  normalize_input_wide.extend(r"\.\file".encode_utf16());
+  let normalize_input = PathBuf::from(OsString::from_wide(&normalize_input_wide));
 
-  let mut expected_wide: Vec<u16> = r"C:\workspace\invalid-".encode_utf16().collect();
-  expected_wide.push(0xd800);
-  expected_wide.extend(r"\file".encode_utf16());
+  let mut normalized_wide: Vec<u16> = r"C:\workspace\invalid-".encode_utf16().collect();
+  normalized_wide.push(0xd800);
+  normalized_wide.extend(r"\file".encode_utf16());
   assert_eq!(
-    input.clone().into_normalized().as_os_str().encode_wide().collect::<Vec<_>>(),
-    expected_wide,
+    normalize_input.into_normalized().as_os_str().encode_wide().collect::<Vec<_>>(),
+    normalized_wide,
   );
-  let returned = input
-    .clone()
-    .try_into_slash()
-    .expect_err("invalid Windows encoding must be returned unchanged");
+
+  let mut input_wide: Vec<u16> = r".\dir\\invalid-".encode_utf16().collect();
+  input_wide.push(0xd800);
+  input_wide.extend(r"\..\tail\".encode_utf16());
+  let input = PathBuf::from(OsString::from_wide(&input_wide));
+
+  let strict = input.clone();
+  assert!(std::panic::catch_unwind(move || strict.into_slash()).is_err());
+
+  let recoverable = input.clone();
+  let returned =
+    recoverable.try_into_slash().expect_err("invalid Windows encoding must be returned unchanged");
   assert_eq!(returned.as_os_str().encode_wide().collect::<Vec<_>>(), input_wide);
-  assert_eq!(input.into_slash_lossy(), "C:/workspace/invalid-\u{fffd}/./file");
+  assert_eq!(input.into_slash_lossy(), "./dir//invalid-\u{fffd}/../tail/");
+
+  let mut no_native_separator_wide: Vec<u16> = "invalid-".encode_utf16().collect();
+  no_native_separator_wide.push(0xd800);
+  no_native_separator_wide.extend("/tail".encode_utf16());
+  let no_native_separator = PathBuf::from(OsString::from_wide(&no_native_separator_wide));
+  assert_eq!(no_native_separator.into_slash_lossy(), "invalid-\u{fffd}/tail");
 }
diff --git a/tests/to_slash.rs b/tests/to_slash.rs
index 12e1477..0715246 100644
--- a/tests/to_slash.rs
+++ b/tests/to_slash.rs
@@ -1,53 +1,132 @@
+use std::{
+  borrow::Cow,
+  path::{Path, PathBuf},
+};
+
+use sugar_path::SugarPath;
+
+fn assert_cow_result(
+  result: Cow<'_, str>,
+  source: &str,
+  expected: &str,
+  expect_borrowed: bool,
+  receiver: &str,
+  policy: &str,
+) {
+  assert_eq!(result, expected, "{receiver}/{policy}: input {source:?}");
+
+  match result {
+    Cow::Borrowed(actual) => {
+      assert!(expect_borrowed, "{receiver}/{policy} unexpectedly borrowed: input {source:?}");
+      assert_eq!(actual.as_ptr(), source.as_ptr(), "{receiver}/{policy}: input {source:?}");
+      assert_eq!(actual.len(), source.len(), "{receiver}/{policy}: input {source:?}");
+    }
+    Cow::Owned(_) => {
+      assert!(!expect_borrowed, "{receiver}/{policy} unexpectedly allocated: input {source:?}");
+    }
+  }
+}
+
+fn assert_policies<'a>(
+  receiver: &str,
+  source: &'a str,
+  strict: Cow<'a, str>,
+  fallible: Option<Cow<'a, str>>,
+  lossy: Cow<'a, str>,
+  expected: &str,
+  expect_borrowed: bool,
+) {
+  assert_cow_result(strict, source, expected, expect_borrowed, receiver, "strict");
+  assert_cow_result(
+    fallible.expect("the fixture is valid UTF-8"),
+    source,
+    expected,
+    expect_borrowed,
+    receiver,
+    "try",
+  );
+  assert_cow_result(lossy, source, expected, expect_borrowed, receiver, "lossy");
+}
+
+fn assert_valid_case(input: &str, expected: &str, expect_borrowed: bool) {
+  assert_policies(
+    "str",
+    input,
+    input.to_slash(),
+    input.try_to_slash(),
+    input.to_slash_lossy(),
+    expected,
+    expect_borrowed,
+  );
+
+  let string = input.to_owned();
+  assert_policies(
+    "String",
+    &string,
+    string.to_slash(),
+    string.try_to_slash(),
+    string.to_slash_lossy(),
+    expected,
+    expect_borrowed,
+  );
+
+  let path = Path::new(input);
+  let source = path.to_str().expect("the fixture is valid UTF-8");
+  assert_policies(
+    "Path",
+    source,
+    path.to_slash(),
+    path.try_to_slash(),
+    path.to_slash_lossy(),
+    expected,
+    expect_borrowed,
+  );
+
+  let path_buf = PathBuf::from(input);
+  let source = path_buf.to_str().expect("the fixture is valid UTF-8");
+  assert_policies(
+    "PathBuf",
+    source,
+    path_buf.to_slash(),
+    path_buf.try_to_slash(),
+    path_buf.to_slash_lossy(),
+    expected,
+    expect_borrowed,
+  );
+}
+
 #[cfg(target_family = "unix")]
 #[test]
-fn unix() {
-  use std::borrow::Cow;
-  use sugar_path::SugarPath;
-
+fn unix_valid_receiver_and_policy_matrix_is_exact_and_borrowed() {
   let cases = [
     ("hello/world", "hello/world"),
-    ("hello/world/", "hello/world/"),
-    ("/hello/world", "/hello/world"),
-    ("/hello/world/", "/hello/world/"),
-    ("/hello\\world", "/hello\\world"),
+    (r"/root/./β/../tail//literal\name//", r"/root/./β/../tail//literal\name//"),
   ];
 
-  for (input, right) in cases {
-    let strict = input.to_slash();
-    let lossy = input.to_slash_lossy();
-    assert!(matches!(strict, Cow::Borrowed(_)), "strict result should borrow: {input:#?}");
-    assert!(matches!(lossy, Cow::Borrowed(_)), "lossy result should borrow: {input:#?}");
-    assert_eq!(strict, right, "case: {input:#?}");
-    assert_eq!(lossy, right, "case: {input:#?}");
+  for (input, expected) in cases {
+    assert_valid_case(input, expected, true);
   }
 }
 
 #[cfg(target_family = "windows")]
 #[test]
-fn windows() {
-  use std::borrow::Cow;
-  use sugar_path::SugarPath;
-
+fn windows_valid_receiver_and_policy_matrix_preserves_spelling() {
   let cases = [
-    ("hello\\world", "hello/world"),
-    ("hello\\world\\", "hello/world/"),
-    ("c:hello\\world", "c:hello/world"),
-    ("c:hello\\world\\", "c:hello/world/"),
-    ("c:\\hello\\world", "c:/hello/world"),
-    ("c:\\hello\\world/", "c:/hello/world/"),
+    (r"c:hello\world\", "c:hello/world/", false),
+    (r"C:\hello\world\", "C:/hello/world/", false),
+    (
+      r"\\server\share\.\β\..\tail\\foreign/name\\",
+      "//server/share/./β/../tail//foreign/name//",
+      false,
+    ),
+    (
+      "//server/share/./β/../tail//foreign/name//",
+      "//server/share/./β/../tail//foreign/name//",
+      true,
+    ),
   ];
 
-  for (input, right) in cases {
-    let strict = input.to_slash();
-    let lossy = input.to_slash_lossy();
-    assert!(matches!(strict, Cow::Owned(_)), "strict result should own: {input:#?}");
-    assert!(matches!(lossy, Cow::Owned(_)), "lossy result should own: {input:#?}");
-    assert_eq!(strict, right, "case: {input:#?}");
-    assert_eq!(lossy, right, "case: {input:#?}");
+  for (input, expected, expect_borrowed) in cases {
+    assert_valid_case(input, expected, expect_borrowed);
   }
-
-  let slash_only = "C:/hello/world";
-  assert!(matches!(slash_only.to_slash(), Cow::Borrowed(_)));
-  assert!(matches!(slash_only.try_to_slash(), Some(Cow::Borrowed(_))));
-  assert!(matches!(slash_only.to_slash_lossy(), Cow::Borrowed(_)));
 }