Challenge 2 — Solution

Task: Using the Chapter 3 InsufficientFundsException-style BankAccount
class from Intermediate Chapter 3, write a PHPUnit test that uses
expectException() to confirm withdrawing more than the balance throws
InsufficientFundsException, and a second test confirming a valid
withdrawal correctly reduces the balance.

---- src/BankAccount.php (from Intermediate Chapter 3) ----

<?php
class InsufficientFundsException extends Exception {}

class BankAccount {
    private float $balance = 0;

    public function deposit(float $amount) {
        $this->balance += $amount;
    }

    public function withdraw(float $amount) {
        if ($amount > $this->balance) {
            throw new InsufficientFundsException("Cannot withdraw £$amount, balance is only £{$this->balance}");
        }
        $this->balance -= $amount;
    }

    public function getBalance(): float {
        return $this->balance;
    }
}

---- tests/BankAccountTest.php ----

<?php
use PHPUnit\Framework\TestCase;

class BankAccountTest extends TestCase {
    public function testWithdrawMoreThanBalanceThrowsException() {
        $account = new BankAccount();
        $account->deposit(50);

        $this->expectException(InsufficientFundsException::class);
        $account->withdraw(100);
    }

    public function testValidWithdrawalReducesBalance() {
        $account = new BankAccount();
        $account->deposit(100);
        $account->withdraw(30);

        $this->assertEquals(70, $account->getBalance());
    }
}


Expected test run output:
PHPUnit 10.x

..                                                                   2 / 2 (100%)

OK (2 tests, 2 assertions)

Notes:
- The first test deliberately deposits 50 before attempting to
  withdraw 100, ensuring the InsufficientFundsException genuinely comes
  from the amount exceeding the balance, not from some unrelated
  problem with an empty account.
- expectException() must be called BEFORE the line that's actually
  expected to throw - PHPUnit records the expectation first, then
  verifies it was met once the throwing line executes.
- The second test verifies the withdrawal actually changed state
  correctly (100 - 30 = 70), using getBalance() as the only way to
  inspect the account's own private $balance property from outside the
  class - exactly the encapsulation pattern from Intermediate Chapter
  2, now being exercised by an automated test rather than a manual
  echo.