Add integration tests running bat with empty input files.

[reidwagner]

Relates to discussion on PR #492.

[sharkdp]

Thank you very much!

One thing I noticed after releasing 0.10 is that there is a change in behavior with your implementation in #492 regarding empty files:

If you call bat test.txt empty.txt test.txt on an interactive terminal (where it prints everything with grid, line numbers, header, etc.), you get this:

▶ bat test.txt empty.txt test.txt 
───────┬───────────────────────────────────────────
       │ File: test.txt
───────┼───────────────────────────────────────────
   1   │ hello world
───────┴───────────────────────────────────────────
───────┬───────────────────────────────────────────
       │ File: test.txt
───────┼───────────────────────────────────────────
   1   │ hello world
───────┴───────────────────────────────────────────

I believe that previous versions of bat would have printed the file header. Like this:

▶ bat test.txt empty.txt test.txt 
───────┬───────────────────────────────────────────
       │ File: test.txt
───────┼───────────────────────────────────────────
   1   │ hello world
───────┴───────────────────────────────────────────
───────┬───────────────────────────────────────────
       │ File: empty.txt
───────┴───────────────────────────────────────────
───────┬───────────────────────────────────────────
       │ File: test.txt
───────┼───────────────────────────────────────────
   1   │ hello world
───────┴───────────────────────────────────────────

It's not really that important, but I think it would be nice to get this behavior back. To check for this in an integration test, we could call something like:

bat --style=header --decorations=always empty.txt

and make sure that the header is there.

[reidwagner]

Ah, I didn't notice that. I'll take a look ASAP. Thanks!