[remcotolsma]

Summary

Adds currency validation to Money::add() and Money::subtract() — operations on Money objects with different currencies now throw a CurrencyMismatchException instead of silently using the first operand's currency.

Changes

• New class CurrencyMismatchException — extends \InvalidArgumentException with a descriptive message showing both currency codes.
• Money::add() — throws if the addend has a different currency.
• Money::subtract() — throws if the subtrahend has a different currency.
• Tests — added test_add_currency_mismatch and test_subtract_currency_mismatch.

This follows the same pattern as moneyphp/money.

Closes #11

[gemini-code-assist]

Code Review

This pull request introduces a new CurrencyMismatchException and updates the add and subtract methods in the Money class to throw this exception when performing operations on objects with mismatched currencies. Corresponding unit tests have also been added. The feedback suggests improving these tests by asserting the specific exception message in addition to the exception class to prevent false positives.

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[gemini-code-assist]

It is highly recommended to assert the exception message in addition to the exception class. This ensures that the exception is thrown with the expected message and details (e.g., the specific currency codes), preventing false positives in tests.

	public function test_add_currency_mismatch() {
		$this->expectException( CurrencyMismatchException::class );
		$this->expectExceptionMessage( 'Cannot perform arithmetic operation on Money objects with different currencies: EUR and USD.' );

		$eur = new Money( 100, 'EUR' );
		$usd = new Money( 50, 'USD' );

		$eur->add( $usd );
	}

[gemini-code-assist]

It is highly recommended to assert the exception message in addition to the exception class. This ensures that the exception is thrown with the expected message and details (e.g., the specific currency codes), preventing false positives in tests.

	public function test_subtract_currency_mismatch() {
		$this->expectException( CurrencyMismatchException::class );
		$this->expectExceptionMessage( 'Cannot perform arithmetic operation on Money objects with different currencies: EUR and USD.' );

		$eur = new Money( 100, 'EUR' );
		$usd = new Money( 50, 'USD' );

		$eur->subtract( $usd );
	}