diff --git a/src/checkPassword.js b/src/checkPassword.js
index 1a6fc05..d167503 100644
--- a/src/checkPassword.js
+++ b/src/checkPassword.js
@@ -6,12 +6,21 @@
  * @returns {boolean}
  */
 function checkPassword(password) {
-  // eslint-disable-next-line
-  const validPasswordRegex = /^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[^a-zA-Z0-9])(?!.*\s).{8,16}$/;
-  const cyrillicValidation = /^((?![А-Яа-я]).)*$/;
+  if (typeof password !== 'string') return false;
 
-  // eslint-disable-next-line
-  if (password.match(validPasswordRegex) && password.match(cyrillicValidation)) {
+  // regex sprawdzający:
+  // - co najmniej 1 wielką literę
+  // - co najmniej 1 cyfrę
+  // - co najmniej 1 znak specjalny
+  // - brak spacji
+  // - długość 8-16
+  const validPasswordRegex =
+    /^(?=.*\d)(?=.*[A-Z])(?=.*[^a-zA-Z0-9])(?!.*\s).{8,16}$/;
+
+  // regex sprawdzający tylko znaki ASCII od ! do ~ (bez spacji)
+  const asciiValidation = /^[\x21-\x7E]*$/;
+
+  if (validPasswordRegex.test(password) && asciiValidation.test(password)) {
     return true;
   }
 
@@ -19,3 +28,5 @@ function checkPassword(password) {
 }
 
 module.exports = checkPassword;
+
+
diff --git a/src/checkPassword.test.js b/src/checkPassword.test.js
index 1e77e16..8d4e112 100644
--- a/src/checkPassword.test.js
+++ b/src/checkPassword.test.js
@@ -1,19 +1,75 @@
 'use strict';
 
-describe(`Function 'checkPassword':`, () => {
-  const checkPassword = require('./checkPassword');
+const checkPassword = require('./checkPassword');
 
+describe(`Function 'checkPassword':`, () => {
   it(`should be declared`, () => {
     expect(checkPassword).toBeInstanceOf(Function);
   });
 
-  it(`should return boolean`, () => {
+  it(`should return a boolean`, () => {
+    const result = checkPassword('Password1!');
+    expect(typeof result).toBe('boolean');
+  });
 
+  // README examples
+  it(`should return true for checkPassword('Password1!')`, () => {
+    expect(checkPassword('Password1!')).toBe(true);
   });
 
-  it(`should return 'true' for the valid password with 8 characters`, () => {
+  it(`should return false for checkPassword('qwerty')`, () => {
+    expect(checkPassword('qwerty')).toBe(false);
+  });
 
+  it(`should return false for checkPassword('Str@ng')`, () => {
+    expect(checkPassword('Str@ng')).toBe(false);
   });
 
-  // write more tests here
+  // Length boundaries
+  it(`should return false for 7-character password`, () => {
+    expect(checkPassword('Abcde1!')).toBe(false);
+  });
+
+  it(`should return true for 8-character valid password`, () => {
+    expect(checkPassword('Abcdef1!')).toBe(true);
+  });
+
+  it(`should return true for 16-character valid password`, () => {
+    expect(checkPassword('Abcdefgh1234!XYZ')).toBe(true);
+  });
+
+  it(`should return false for 17-character password`, () => {
+    // 15 liter + 1 cyfra + 1 znak specjalny = 17 znaków
+    expect(checkPassword('Abcdefghijklmno1!')).toBe(false);
+  });
+
+  // Character class coverage
+  it(`should return false for password without uppercase`, () => {
+    expect(checkPassword('abcdef1!')).toBe(false);
+  });
+
+  it(`should return false for password without digit`, () => {
+    expect(checkPassword('Abcdefgh!')).toBe(false);
+  });
+
+  it(`should return false for password without special char`, () => {
+    expect(checkPassword('Abcdefg1')).toBe(false);
+  });
+
+  it(`should return true for uppercase-only valid password`, () => {
+    expect(checkPassword('ABCDEF12!')).toBe(true);
+  });
+
+  it(`should return false for password with Cyrillic letters`, () => {
+    expect(checkPassword('Пароль1!')).toBe(false);
+  });
+
+  it(`should return false for password with accented Latin letters`, () => {
+    expect(checkPassword('Pässword1!')).toBe(false);
+  });
+
+  // Whitespace check
+  it(`should return false for password containing whitespace`, () => {
+    expect(checkPassword('Abc def1!')).toBe(false);
+  });
 });