Repl integration testing

[se7entyse7en]

Closes #334.

I've tested many other possibilities, but I failed with each of them. All the problems derived from two things:

1. make the stdin be recognized as a char mode device here,
2. keep the stdin open so that I can write queries interactively.

• I've tried running the command as /bin/bash -e <path to srcd> sql, but it was exiting as if it was run normally,
• I've tried using os.Stdin as command.Stdin, but it has a couple of problems:
  1. the stdin was correctly recognized as char mode device (obviously),
  2. if I don't write on command.Stdin before starting the command, then stdin was interpreted as closed (or reads EOF) so it just exits immediately
• I've then tried to use a Reader (command.Stdin is a Reader) which is channel-based so that stdin is not interpreted as closed as long as I don't close the channel. This was actually both a Reader and a Writer so that it is used as a Reader by the program and as a Writer by the test to write queries:
  1. the stdin was not interpreted as closed, so I was able to write queries after the command has been started,
  2. the stdin was not recognized as a char mode device, so it was entering in this if,
  3. so what I was writing was actually interpreted as if the input was piped in.
• I've tried using a bytes.Buffer, but it has the same effect, but it was also additionally not recognized as a char mode device.
• I've then tried to improve the previous solution and tried to hack that first read by sending an EOF without closing the channel. I was able to implement it by configuring the Reader to send an EOF when I write a specificied marker (in the previous solution the EOF was being sent only when the underlying channel was closed):
  1. it was hacky, and it wasn't working, I don't even remember what exactly...

Then I discovered that I could actually run a pseudo-terminal. By using a pseudo-terminal the stdin was correctly interpreted as a char mode device, and it was not interpreted as closed immediately.

[se7entyse7en]

I've just realized that I haven't pushed on my fork.

[se7entyse7en]

@smacker all issues you pointed out should have been addressed here. I've extracted a StreamLinifier util that is responsible of yielding lines from a stream of strings.

[smacker]

The only thing I worry about is when sql doesn't return results or returns error. But it's not very important.

[se7entyse7en]

Gonna fix DCO before rebasing and merging.

[se7entyse7en]

Rebased and squashed. I've also added some docs for the StreamLinifier.

Side note: we currently cannot use icmd for testing the interactive SQL REPL. See here. I've created an issue.