diff --git a/.npmignore b/.npmignore
index 4611446..d56ab20 100644
--- a/.npmignore
+++ b/.npmignore
@@ -7,6 +7,9 @@ tests/
 *.config.js
 *.config.mjs
 *.config.ts
+*.test.mjs
+*.test.js
+*.test.ts
 *.tgz
 .editorconfig
 .gitattributes
diff --git a/package.json b/package.json
index d2a12a5..07a39e5 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@phanect/utils",
-  "version": "2.0.4",
+  "version": "3.0.0",
   "description": "@phanect's personal utility library for JavaScript & TypeScript",
   "repository": {
     "type": "git",
diff --git a/test/nodejs/load-json.test.ts b/src/nodejs/load-json.test.ts
similarity index 65%
rename from test/nodejs/load-json.test.ts
rename to src/nodejs/load-json.test.ts
index b3edce0..94e9aa4 100644
--- a/test/nodejs/load-json.test.ts
+++ b/src/nodejs/load-json.test.ts
@@ -1,10 +1,10 @@
 import { join } from "node:path";
 import { expect, test } from "vitest";
-import { loadJSON } from "../../src/nodejs.ts";
+import { loadJSON } from "../nodejs.ts";
 
 test("loadJSON", async () => {
   const obj = await loadJSON(
-    join(import.meta.dirname, "../fixtures/load-json/fixture.json"),
+    join(import.meta.dirname, "../../test/fixtures/load-json/fixture.json"),
   );
 
   expect(obj).toStrictEqual({
diff --git a/src/universal.ts b/src/universal.ts
index 8fe5516..3114f34 100644
--- a/src/universal.ts
+++ b/src/universal.ts
@@ -2,13 +2,7 @@ export { deduplicate } from "./universal/deduplicate.ts";
 export { trimLines } from "./universal/trim-lines.ts";
 export { getLastElementOf } from "./universal/get-last-element-of.ts";
 export { npmPackageExists } from "./universal/npm-package-exists.ts";
-export { random } from "./universal/random.ts";
+export { pseudoRandomInt } from "./universal/pseudo-random-int.ts";
+export { pseudoRandomString } from "./universal/pseudo-random-string.ts";
 export { sleep } from "./universal/sleep.ts";
 export { sortObjects } from "./universal/sort-objects.ts";
-
-//
-// Backward compatibility
-//
-
-/** @deprecated `deindent()` is renamed to `trimLines()` */
-export { trimLines as deindent } from "./universal/trim-lines.ts";
diff --git a/test/universal/deduplicate.test.ts b/src/universal/deduplicate.test.ts
similarity index 91%
rename from test/universal/deduplicate.test.ts
rename to src/universal/deduplicate.test.ts
index 9b534eb..1acad8c 100644
--- a/test/universal/deduplicate.test.ts
+++ b/src/universal/deduplicate.test.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "vitest";
-import { deduplicate } from "../../src/universal.ts";
+import { deduplicate } from "../universal.ts";
 
 test("deduplicate", () => {
   const deduplicated = deduplicate([
diff --git a/test/universal/get-last-element-of.test.ts b/src/universal/get-last-element-of.test.ts
similarity index 96%
rename from test/universal/get-last-element-of.test.ts
rename to src/universal/get-last-element-of.test.ts
index aa56df7..be35f0d 100644
--- a/test/universal/get-last-element-of.test.ts
+++ b/src/universal/get-last-element-of.test.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "vitest";
-import { getLastElementOf } from "../../src/universal.ts";
+import { getLastElementOf } from "../universal.ts";
 
 test("getLastElementOf (without index)", () => {
   const lastElement = getLastElementOf([ "a", "b", "c" ]);
diff --git a/src/universal/pseudo-random-int.test.ts b/src/universal/pseudo-random-int.test.ts
new file mode 100644
index 0000000..f94d260
--- /dev/null
+++ b/src/universal/pseudo-random-int.test.ts
@@ -0,0 +1,56 @@
+import { ok } from "node:assert";
+import { describe, expect, test } from "vitest";
+import { pseudoRandomInt } from "./pseudo-random-int.ts";
+
+describe("pseudoRandomInt()", () => {
+  test("returns a number within valid range", () => {
+    const generatedNumber = pseudoRandomInt(100);
+
+    expect(generatedNumber).toBeLessThanOrEqual(100);
+    expect(generatedNumber).toBeGreaterThanOrEqual(0);
+    expect(typeof generatedNumber).toBe("number");
+  });
+
+  test("returns an integer (no decimals)", () => {
+    const generatedNumber = pseudoRandomInt(100);
+    ok(Number.isInteger(generatedNumber));
+  });
+
+  test("handles max value of 0 (returns 0)", () => {
+    const generatedNumber = pseudoRandomInt(0);
+    expect(generatedNumber).toBe(0);
+  });
+
+  test("returns 0 or 1 for max value of 1", () => {
+    const generatedNumber = pseudoRandomInt(1);
+    expect([ 0, 1 ]).toContain(generatedNumber);
+  });
+
+  test("returns values in expected range for small max", () => {
+    const max = 10;
+    const results = new Set<number>();
+
+    // Generate multiple random numbers to test distribution
+    for (let i = 0; i < 100; i++) {
+      const generatedNumber = pseudoRandomInt(max);
+      results.add(generatedNumber);
+      expect(generatedNumber).toBeGreaterThanOrEqual(0);
+      expect(generatedNumber).toBeLessThanOrEqual(max);
+      expect(Number.isInteger(generatedNumber)).toBe(true);
+    }
+
+    // Should generate at least some variety in 100 attempts
+    expect(results.size).toBeGreaterThan(1);
+  });
+
+  test("returns values in expected range for large max", () => {
+    const max = 1000000;
+
+    for (let i = 0; i < 100; i++) {
+      const generatedNumber = pseudoRandomInt(max);
+      expect(generatedNumber).toBeGreaterThanOrEqual(0);
+      expect(generatedNumber).toBeLessThanOrEqual(max);
+      expect(Number.isInteger(generatedNumber)).toBe(true);
+    }
+  });
+});
diff --git a/src/universal/pseudo-random-int.ts b/src/universal/pseudo-random-int.ts
new file mode 100644
index 0000000..742eda7
--- /dev/null
+++ b/src/universal/pseudo-random-int.ts
@@ -0,0 +1,13 @@
+/**
+ * Generates pseudo-random non-negative integer number.
+ * Don't use this function for security purpose. (e.g., generating password)
+ * @param max - max number of the generated random number
+ * @returns pseudo-random non-negative integer number
+ */
+export const pseudoRandomInt = (max: number): number => {
+  if (!Number.isFinite(max) || max < 0) {
+    throw new RangeError("max must be a finite, non-negative number");
+  }
+
+  return Math.floor(Math.random() * (max + 1));
+};
diff --git a/src/universal/pseudo-random-string-chars.ts b/src/universal/pseudo-random-string-chars.ts
new file mode 100644
index 0000000..7ede00a
--- /dev/null
+++ b/src/universal/pseudo-random-string-chars.ts
@@ -0,0 +1,9 @@
+export const chars = [
+  "A", "B", "C", "D", "E", "F", "G", "H", "I", "J",
+  "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T",
+  "U", "V", "W", "X", "Y", "Z",
+  "a", "b", "c", "d", "e", "f", "g", "h", "i", "j",
+  "k", "l", "m", "n", "o", "p", "q", "r", "s", "t",
+  "u", "v", "w", "x", "y", "z",
+  "0", "1", "2", "3", "4", "5", "6", "7", "8", "9",
+] as const;
diff --git a/src/universal/pseudo-random-string.test.ts b/src/universal/pseudo-random-string.test.ts
new file mode 100644
index 0000000..100b692
--- /dev/null
+++ b/src/universal/pseudo-random-string.test.ts
@@ -0,0 +1,53 @@
+import { describe, expect, test } from "vitest";
+import { pseudoRandomInt } from "./pseudo-random-int.ts";
+import { pseudoRandomString } from "./pseudo-random-string.ts";
+
+describe("pseudoRandomString()", () => {
+  test("returns a string with the correct length", () => {
+    const generatedString = pseudoRandomString(10);
+
+    expect(generatedString).toHaveLength(10);
+    expect(typeof generatedString).toBe("string");
+  });
+
+  test("returns different strings on multiple calls", () => {
+    const generatedString1 = pseudoRandomString(20);
+    const generatedString2 = pseudoRandomString(20);
+    const generatedString3 = pseudoRandomString(20);
+
+    expect(generatedString1).not.toBe(generatedString2);
+    expect(generatedString2).not.toBe(generatedString3);
+    expect(generatedString1).not.toBe(generatedString3);
+  });
+
+  test("throws an Error when length is 0", () =>
+    expect(() => pseudoRandomString(0)).toThrowError()
+  );
+
+  test("throws an Error when length is a negative number", () =>
+    expect(() => pseudoRandomString(-4)).toThrowError()
+  );
+
+  test("generates string with only valid characters (alphanumeric)", () => {
+    const generatedString = pseudoRandomString(100);
+    expect(generatedString).toMatch(/^[A-Za-z0-9]+$/);
+  });
+
+  test("works with different length values", () => {
+    for (const length of Array.from({ length: 5 }, () => pseudoRandomInt(500) + 1)) {
+      const generatedString = pseudoRandomString(length);
+      expect(generatedString).toHaveLength(length);
+      expect(typeof generatedString).toBe("string");
+    }
+  });
+
+  test("generates strings with good distribution of characters", () => {
+    // Generate a long string and check that multiple different characters appear
+    const generatedString = pseudoRandomString(1000);
+    const uniqueChars = new Set(generatedString.split(""));
+
+    // With 1000 characters, we should see a good variety
+    // (at least 40 different characters out of 62 possible)
+    expect(uniqueChars.size).toBeGreaterThan(40);
+  });
+});
diff --git a/src/universal/pseudo-random-string.ts b/src/universal/pseudo-random-string.ts
new file mode 100644
index 0000000..6b802a5
--- /dev/null
+++ b/src/universal/pseudo-random-string.ts
@@ -0,0 +1,19 @@
+import { pseudoRandomInt } from "./pseudo-random-int.ts";
+import { chars } from "./pseudo-random-string-chars.ts";
+
+/**
+ * Generates pseudo-random string.
+ * Don't use this function for security purpose. (e.g., generating password)
+ * @param length - length of the generated string
+ * @returns pseudo-random string
+ */
+export const pseudoRandomString = (length: number): string => {
+  if (!Number.isInteger(length) || length <= 0) {
+    throw new Error(`\`length\` must be a natural number, but \`${ length }\` is given.`);
+  }
+
+  return Array.from({ length }, () => {
+    const index = pseudoRandomInt(chars.length - 1);
+    return chars[index];
+  }).join("");
+};
diff --git a/src/universal/random.ts b/src/universal/random.ts
deleted file mode 100644
index 33f607f..0000000
--- a/src/universal/random.ts
+++ /dev/null
@@ -1,6 +0,0 @@
-/**
- * Generates random integer number.
- * @param max - max number of the generated random number
- * @returns random number (integer)
- */
-export const random = (max: number): number => Math.floor(Math.random() * max);
diff --git a/test/universal/sleep.test.ts b/src/universal/sleep.test.ts
similarity index 84%
rename from test/universal/sleep.test.ts
rename to src/universal/sleep.test.ts
index de45f40..c6c7028 100644
--- a/test/universal/sleep.test.ts
+++ b/src/universal/sleep.test.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "vitest";
-import { sleep } from "../../src/universal.ts";
+import { sleep } from "../universal.ts";
 
 test("sleep", async () => {
   const startAt = new Date();
diff --git a/test/universal/sort-objects.test.ts b/src/universal/sort-objects.test.ts
similarity index 84%
rename from test/universal/sort-objects.test.ts
rename to src/universal/sort-objects.test.ts
index ac46f05..d40f12c 100644
--- a/test/universal/sort-objects.test.ts
+++ b/src/universal/sort-objects.test.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "vitest";
-import { sortObjects } from "../../src/universal.ts";
+import { sortObjects } from "../universal.ts";
 
 test("sortObjects", () => {
   const result = sortObjects([
diff --git a/test/universal/deindent.test.ts b/src/universal/trim-lines.test.ts
similarity index 72%
rename from test/universal/deindent.test.ts
rename to src/universal/trim-lines.test.ts
index 10dc789..86f448f 100644
--- a/test/universal/deindent.test.ts
+++ b/src/universal/trim-lines.test.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "vitest";
-import { deindent } from "../../src/universal.ts";
+import { trimLines } from "../universal.ts";
 
 test("deindent", () => {
   const before = `
@@ -11,7 +11,7 @@ test("deindent", () => {
 "test": "JS object"
 }`;
 
-  const actualAfter = deindent(before);
+  const actualAfter = trimLines(before);
 
   expect(actualAfter).toStrictEqual(expectedAfter);
 }, 10000);