5 0.2 0.2 / 0.2)`);

    // Testing with calc().
    test_valid_value(`color`, `oklab(from oklab(0.25 0.2 0.5) calc(l) calc(a) calc(b))`, `oklab(0.25 0.2 0.5)`);
    test_valid_value(`color`, `oklab(from oklab(0.25 0.2 0.5 / 40%) calc(l) calc(a) calc(b) / calc(alpha))`, `oklab(0.25 0.2 0.5 / 0.4)`);

    // Testing with 'none'.
    test_valid_value(`color`, `oklab(from oklab(0.25 0.2 0.5) none none none)`, `oklab(none none none)`);
    test_valid_value(`color`, `oklab(from oklab(0.25 0.2 0.5) none none none