Re: [PATCH v4] diff: make diff_free_filespec_data accept NULL

> +test_expect_success 'difftool --cached with unmerged files' '
> +	test_when_finished git reset --hard &&
> +	echo base >file &&
> +	git add file &&
> +	git commit -m base &&
> 
> This does not advance the committer date. Let's just use the helper
> function we invented to make this much easier:
> 
> 	test_commit base
> 
> This has also the advantage of already tagging the outcome.
> 
>> +	git checkout -B conflict-a &&
>> +	git checkout -B conflict-b &&
>> +	git checkout conflict-a &&
>> +	echo conflict-a >>file &&
>> +	git add file &&
>> +	git commit -m conflict-a &&
>> +	git checkout conflict-b &&
>> +	echo conflict-b >>file &&
>> +	git add file &&
>> +	git commit -m conflict-b &&
>> +	git checkout master &&
>> +	git merge conflict-a &&
>> +	test_must_fail git merge conflict-b &&
>> +	: >expect &&
>> +	git difftool --cached --no-prompt >actual &&
>> +	test_cmp expect actual
> 
> Shouldn't this use the `test_must_be_empty` function instead?
> 
> How about writing the test case this way:
> 
> test_expect_success 'difftool --cached with unmerged files' '
> 	test_when_finished git reset --hard &&
> 
> 	test_commit conflicting &&
> 	test_commit conflict-a a conflicting.t &&
> 	git reset --hard conflicting &&
> 	test_commit conflict-b b conflicting.t &&
> 	test_must_fail git merge conflict-a &&
> 
> 	git difftool --cached --no-prompt >out &&
> 	test_must_be_empty out
> '