The code is doing "if (!double_buf_equal () != 0)" which seems to be a
convoluted way to do "if (!double_buf_equal ())". Fixes:

../test/pattern-getters.c:153:6: warning: logical not is only applied to the left hand side of this comparison [-Wlogical-not-parentheses]
        if (!double_buf_equal (ctx, new_buf, expected_values,
            ^
../test/pattern-getters.c:153:6: note: add parentheses after the '!' to evaluate the comparison first
        if (!double_buf_equal (ctx, new_buf, expected_values,
            ^
             (
../test/pattern-getters.c:153:6: note: add parentheses around left hand side expression to silence this warning
        if (!double_buf_equal (ctx, new_buf, expected_values,
            ^
            (