Unit Tests: Clear cart notices in test_fixed_cart_discount method

tests/unit-tests/cart.php

@@ -506,6 +506,9 @@ class WC_Tests_Cart extends WC_Unit_Test_Case {
 		// Test if the cart total amount is equal 5
 		$this->assertEquals( 5, WC()->cart->total );
 
+		// Clearing WC notices
+		wc_clear_notices();
+
 		// Clean up the cart
 		WC()->cart->empty_cart();