How to fix AssertionError: Assertion failed (assert.strictEqual failed) in Node.js

AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:
+ actual - expected

+ 'hello'
- 'Hello'

const actual = functionUnderTest();
const expected = 42;

console.log('Actual:', actual, typeof actual);    // "42" string
console.log('Expected:', expected, typeof expected);  // 42 number

// This will fail:
assert.strictEqual(actual, expected);

// Fix: Convert to same type
assert.strictEqual(Number(actual), expected);
// OR
assert.strictEqual(actual, String(expected));

// This FAILS with strictEqual (compares references):
const actual = [1, 2, 3];
const expected = [1, 2, 3];
assert.strictEqual(actual, expected);  // AssertionError

// This PASSES with deepStrictEqual (compares content):
assert.deepStrictEqual(actual, expected);  // ✓

// Also works for objects:
const user = { name: 'Alice', age: 30 };
const expectedUser = { name: 'Alice', age: 30 };
assert.deepStrictEqual(user, expectedUser);  // ✓

// Example: Function returns wrong value
function calculateTotal(items) {
  return items.reduce((sum, item) => sum + item.price, 0);
}

// Test fails because function doesn't handle empty arrays
const result = calculateTotal([]);
assert.strictEqual(result, 0);  // Passes

// But if function had a bug:
function calculateTotalBuggy(items) {
  return items.reduce((sum, item) => sum + item.price);  // No initial value!
}

const buggyResult = calculateTotalBuggy([]);
assert.strictEqual(buggyResult, 0);  // FAILS - returns undefined

// Fix: Add initial value or handle empty case

// WRONG: Assertion runs before async operation completes
function testAsync() {
  let result;
  fetchData().then(data => result = data);
  assert.strictEqual(result, 'expected');  // FAILS - result is undefined
}

// CORRECT: Use async/await
async function testAsyncCorrect() {
  const result = await fetchData();
  assert.strictEqual(result, 'expected');  // Waits for data
}

// OR: Use callbacks/promises properly
function testAsyncCallback(done) {
  fetchData().then(data => {
    assert.strictEqual(data, 'expected');
    done();
  });
}