lab(from lab(25 20 50 / 40%) l b a)`, `lab(25 50 20 / 0.4)`);
    test_valid_value(`color`, `lab(from lab(25 20 50 / 40%) l a a / a)`, `lab(25 20 20)`);

    // Testing with calc().
    test_valid_value(`color`, `lab(from lab(25 20 50) calc(l) calc(a) calc(b))`, `lab(25 20 50)`);
    test_valid_value(`color`, `lab(from lab(25 20 50 / 40%) calc(l) calc(a) calc(b) / calc(alpha))`, `lab(25 20 50 / 0.4)`);

    // Testing with 'none'.
    test_valid_value(`color`, `lab(from lab(25 20 50) none none none)`, `lab(