diff --git a/path/_common/assert_path_test.ts b/path/_common/assert_path_test.ts
new file mode 100644
index 000000000000..cf2161eea113
--- /dev/null
+++ b/path/_common/assert_path_test.ts
@@ -0,0 +1,17 @@
+// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
+
+import { assertEquals, assertThrows } from "@std/assert";
+import { assertPath } from "./assert_path.ts";
+
+Deno.test("assertPath()", () => {
+  assertEquals(assertPath(""), undefined);
+  assertEquals(assertPath("foo"), undefined);
+});
+
+Deno.test("assertPath() throws", () => {
+  assertThrows(
+    () => assertPath(undefined),
+    TypeError,
+    "Path must be a string. Received undefined",
+  );
+});
diff --git a/path/_common/basename_test.ts b/path/_common/basename_test.ts
new file mode 100644
index 000000000000..71961fa1cd86
--- /dev/null
+++ b/path/_common/basename_test.ts
@@ -0,0 +1,49 @@
+// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
+
+import { assertEquals, assertThrows } from "@std/assert";
+import { assertArgs, lastPathSegment, stripSuffix } from "./basename.ts";
+import { CHAR_FORWARD_SLASH } from "./constants.ts";
+
+Deno.test("assertArgs()", () => {
+  assertEquals(assertArgs("", ""), "");
+  assertEquals(assertArgs("foo", "bar"), undefined);
+  // @ts-expect-error - testing invalid input for suffix
+  assertEquals(assertArgs("", undefined), "");
+});
+
+Deno.test("assertArgs() throws", () => {
+  assertThrows(
+    // @ts-expect-error - testing invalid input
+    () => assertArgs(undefined, "bar"),
+    TypeError,
+    "Path must be a string. Received undefined",
+  );
+  assertThrows(
+    // @ts-expect-error - testing invalid input
+    () => assertArgs("foo", undefined),
+    TypeError,
+    "Suffix must be a string. Received undefined",
+  );
+});
+
+Deno.test("lastPathSegment()", () => {
+  assertEquals(
+    lastPathSegment("foo", (char) => char === CHAR_FORWARD_SLASH),
+    "foo",
+  );
+  assertEquals(
+    lastPathSegment("foo/bar", (char) => char === CHAR_FORWARD_SLASH),
+    "bar",
+  );
+  assertEquals(
+    lastPathSegment("foo/bar/baz", (char) => char === CHAR_FORWARD_SLASH),
+    "baz",
+  );
+});
+
+Deno.test("stripSuffix()", () => {
+  assertEquals(stripSuffix("foo", "bar"), "foo");
+  assertEquals(stripSuffix("foobar", "bar"), "foo");
+  assertEquals(stripSuffix("foobar", "baz"), "foobar");
+  assertEquals(stripSuffix("foobar", "foobar"), "foobar");
+});
diff --git a/path/_common/format_test.ts b/path/_common/format_test.ts
new file mode 100644
index 000000000000..fd1ee971c389
--- /dev/null
+++ b/path/_common/format_test.ts
@@ -0,0 +1,54 @@
+// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
+
+import { assertEquals, assertThrows } from "@std/assert";
+import { _format, assertArg } from "./format.ts";
+
+Deno.test("_format()", () => {
+  assertEquals(_format("", {}), "");
+  assertEquals(_format("", { root: "/" }), "/");
+  assertEquals(_format("", { dir: "/foo/bar" }), "/foo/bar");
+  assertEquals(_format("", { base: "baz" }), "baz");
+  assertEquals(_format("", { name: "baz" }), "baz");
+  assertEquals(_format("", { ext: ".js" }), ".js");
+  assertEquals(_format("", { name: "baz", ext: ".js" }), "baz.js");
+  assertEquals(_format("", { root: "/", base: "baz" }), "/baz");
+  assertEquals(_format("", { root: "/", name: "baz" }), "/baz");
+  assertEquals(_format("", { root: "/", ext: ".js" }), "/.js");
+  assertEquals(_format("", { root: "/", name: "baz", ext: ".js" }), "/baz.js");
+  assertEquals(_format("/", { dir: "/foo/bar", base: "baz" }), "/foo/bar/baz");
+  assertEquals(
+    _format("/", { dir: "/foo/bar", base: "baz", ext: ".js" }),
+    "/foo/bar/baz",
+  );
+  assertEquals(
+    _format("/", { dir: "/foo/bar", name: "baz", ext: ".js" }),
+    "/foo/bar/baz.js",
+  );
+});
+
+Deno.test("assertArg()", () => {
+  assertEquals(assertArg({}), undefined);
+  assertEquals(assertArg({ root: "/" }), undefined);
+  assertEquals(assertArg({ dir: "/foo/bar" }), undefined);
+});
+
+Deno.test("assertArg() throws", () => {
+  assertThrows(
+    // @ts-expect-error - testing invalid input
+    () => assertArg(null),
+    TypeError,
+    `The "pathObject" argument must be of type Object. Received type object`,
+  );
+  assertThrows(
+    // @ts-expect-error - testing invalid input
+    () => assertArg(undefined),
+    TypeError,
+    `The "pathObject" argument must be of type Object. Received type undefined`,
+  );
+  assertThrows(
+    // @ts-expect-error - testing invalid input
+    () => assertArg(""),
+    TypeError,
+    `The "pathObject" argument must be of type Object. Received type string`,
+  );
+});
diff --git a/path/_common/glob_to_reg_exp.ts b/path/_common/glob_to_reg_exp.ts
index ae2274b5bf3d..8b18fde0ca2a 100644
--- a/path/_common/glob_to_reg_exp.ts
+++ b/path/_common/glob_to_reg_exp.ts
@@ -27,7 +27,7 @@ export interface GlobOptions {
 /** Options for {@linkcode globToRegExp}. */
 export type GlobToRegExpOptions = GlobOptions;
 
-const regExpEscapeChars = [
+const REG_EXP_ESCAPE_CHARS = [
   "!",
   "$",
   "(",
@@ -42,8 +42,12 @@ const regExpEscapeChars = [
   "^",
   "{",
   "|",
-];
-const rangeEscapeChars = ["-", "\\", "]"];
+] as const;
+const RANGE_ESCAPE_CHARS = ["-", "\\", "]"] as const;
+
+type RegExpEscapeChar = typeof REG_EXP_ESCAPE_CHARS[number];
+type RangeEscapeChar = typeof RANGE_ESCAPE_CHARS[number];
+type EscapeChar = RegExpEscapeChar | RangeEscapeChar;
 
 export interface GlobConstants {
   sep: string;
@@ -88,8 +92,12 @@ export function _globToRegExp(
     for (; i < glob.length && !c.seps.includes(glob[i]!); i++) {
       if (inEscape) {
         inEscape = false;
-        const escapeChars = inRange ? rangeEscapeChars : regExpEscapeChars;
-        segment += escapeChars.includes(glob[i]!) ? `\\${glob[i]}` : glob[i];
+        const escapeChars = (inRange
+          ? RANGE_ESCAPE_CHARS
+          : REG_EXP_ESCAPE_CHARS) as unknown as EscapeChar[];
+        segment += escapeChars.includes(glob[i]! as EscapeChar)
+          ? `\\${glob[i]}`
+          : glob[i];
         continue;
       }
 
@@ -146,11 +154,7 @@ export function _globToRegExp(
       }
 
       if (inRange) {
-        if (glob[i] === "\\") {
-          segment += `\\\\`;
-        } else {
-          segment += glob[i];
-        }
+        segment += glob[i];
         continue;
       }
 
@@ -252,7 +256,7 @@ export function _globToRegExp(
         continue;
       }
 
-      segment += regExpEscapeChars.includes(glob[i]!)
+      segment += REG_EXP_ESCAPE_CHARS.includes(glob[i]! as RegExpEscapeChar)
         ? `\\${glob[i]}`
         : glob[i];
     }
@@ -262,7 +266,9 @@ export function _globToRegExp(
       // Parse failure. Take all characters from this segment literally.
       segment = "";
       for (const c of glob.slice(j, i)) {
-        segment += regExpEscapeChars.includes(c) ? `\\${c}` : c;
+        segment += REG_EXP_ESCAPE_CHARS.includes(c as RegExpEscapeChar)
+          ? `\\${c}`
+          : c;
         endsWithSep = false;
       }
     }
@@ -276,10 +282,6 @@ export function _globToRegExp(
     // Terminates with `i` at the start of the next segment.
     while (c.seps.includes(glob[i]!)) i++;
 
-    // Check that the next value of `j` is indeed higher than the current value.
-    if (!(i > j)) {
-      throw new Error("Assertion failure: i > j (potential infinite loop)");
-    }
     j = i;
   }
 
diff --git a/path/_common/normalize_string_test.ts b/path/_common/normalize_string_test.ts
new file mode 100644
index 000000000000..8ea883a7dbcf
--- /dev/null
+++ b/path/_common/normalize_string_test.ts
@@ -0,0 +1,26 @@
+// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
+
+import { assertEquals } from "@std/assert";
+import { CHAR_FORWARD_SLASH } from "./constants.ts";
+import { normalizeString } from "./normalize_string.ts";
+
+function isSeparator(code: number): boolean {
+  return code === CHAR_FORWARD_SLASH;
+}
+
+Deno.test("normalizeSring()", () => {
+  assertEquals(normalizeString("", true, "/", isSeparator), "");
+  assertEquals(normalizeString("", false, "/", isSeparator), "");
+  assertEquals(normalizeString("a/../b", true, "/", isSeparator), "b");
+  assertEquals(normalizeString("foo/bar/", true, "/", isSeparator), "foo/bar");
+  assertEquals(normalizeString("/foo/bar", true, "/", isSeparator), "foo/bar");
+  assertEquals(normalizeString("./foo/bar", true, "/", isSeparator), "foo/bar");
+  assertEquals(
+    normalizeString("../foo/bar/baz/", true, "/", isSeparator),
+    "../foo/bar/baz",
+  );
+  assertEquals(
+    normalizeString("/foo/../../bar", true, "/", isSeparator),
+    "../bar",
+  );
+});
diff --git a/path/_common/to_file_url_test.ts b/path/_common/to_file_url_test.ts
new file mode 100644
index 000000000000..a098bc9dcd1c
--- /dev/null
+++ b/path/_common/to_file_url_test.ts
@@ -0,0 +1,21 @@
+// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
+
+import { assertEquals } from "@std/assert";
+import { encodeWhitespace } from "./to_file_url.ts";
+
+Deno.test("encodeWhitespace()", () => {
+  assertEquals(encodeWhitespace("foo"), "foo");
+  assertEquals(encodeWhitespace("foo\tbar"), "foo%09bar");
+  assertEquals(encodeWhitespace("foo\nbar"), "foo%0Abar");
+  assertEquals(encodeWhitespace("foo\vbar"), "foo%0Bbar");
+  assertEquals(encodeWhitespace("foo\fbar"), "foo%0Cbar");
+  assertEquals(encodeWhitespace("foo\rbar"), "foo%0Dbar");
+  assertEquals(encodeWhitespace("foo bar"), "foo%20bar");
+  assertEquals(encodeWhitespace("foo\u0009bar"), "foo%09bar");
+  assertEquals(encodeWhitespace("foo\u000Abar"), "foo%0Abar");
+  assertEquals(encodeWhitespace("foo\u000Bbar"), "foo%0Bbar");
+  assertEquals(encodeWhitespace("foo\u000Cbar"), "foo%0Cbar");
+  assertEquals(encodeWhitespace("foo\u000Dbar"), "foo%0Dbar");
+  assertEquals(encodeWhitespace("foo\u0020bar"), "foo%20bar");
+  assertEquals(encodeWhitespace("foo\ufeffbar"), "foobar");
+});