test: Pick platform randomly in "sloppy" mode.

[WesleyAC]

This will give us more coverage of android when we're running tools/test
in sloppy mode (which is the default).

This does make things somewhat flaky, but on the whole it makes us more
likely to notice failures that only occur on one platform sooner.

[chrisbobbe]

Hmm, in ten runs, I got iOS nine times and Android just once:

chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: ios
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: ios
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: ios
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: ios
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: android
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: ios
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: ios
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: ios
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: ios
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: ios
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!

Could the randomness algorithm be wrong, or should I go buy a lottery ticket?

(I think the probability of one head and nine tails in a coin-flip is 10 * 0.5^10 = 0.009765625. I plugged numbers into the "formula for binomial probabilities" and simplified; 10 * 0.5^10 also makes sense intuitively because the probability of ten coin-flips in order matching a given sequence is 0.5^10, and there are 10 possible sequences that have a sum of one head and nine tails.)

[chrisbobbe]

OK, after ten more runs, this is looking better 🙂:

chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: android
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: ios
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: android
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: ios
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: android
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: android
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: android
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: android
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: ios
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!
chrisbobbe:~/dev/zulip-mobile (master u+1) 
$ tools/test jest
Running jest...
Running one project: ios
No tests found related to files changed since "refs/remotes/upstream/master".
Run Jest without `-o` or with `--all` to run all tests.
Passed!

[chrisbobbe]

So, looks mostly good! In the commit message, let's link to prior discussion (looks like #4700 (comment)), so that's discoverable.

Also shellcheck tools/test has some new output:

In tools/test line 230:
        sloppy) jest_args+=( --selectProjects $RANDOM_PLATFORM);;
                                              ^--------------^ SC2206: Quote to prevent word splitting/globbing, or split robustly with mapfile or read -a.

[WesleyAC]

Fixed the shellcheck and edited the commit message :)

[chrisbobbe]

Thanks! Merged.

[gnprice]

Thanks, this is a useful change.

There were some issues with the shell-scripting style. I've just pushed fixes to those:
c631466 tools/test [nfc]: Use lower case for variables.
988eaa3 tools/test [nfc]: Inline random_platform.
bf5be80 tools/test [nfc]: Drop unnecessary quotes.

Please take a look, including the explanations in the commit messages.

[chrisbobbe]

Oops! Thanks for the fixes. I'll be more careful when reviewing next time; I've just gone and read all those. 🙂