Check that tests exist before trying to build them

[GuillaumeGomez]

I encountered this bug recently in my fork (which adds inline tests and sub-checks): the first time tests are run, they fail because they don't exist. The bug is actually present in your version as well, it's just not as bad as in my fork since the tests are supposed to already exist in your case.

So this fix simply moves the check of the tests existence before trying to build them.

[dtolnay]

I am not clear on what this is fixing. Could you share a way that I could reproduce the incorrect behavior?

[GuillaumeGomez]

Add multiple tests with one that doesn't exist. You'll get the cargo error before you'll get the check_exists error, making the call to check_exists useless in run_all.

[dtolnay]

I tried again and I am still not able to reproduce any test that would produce different behavior before and after this PR.

Please share a complete compilable test.rs, compiler version (stable vs nightly follow slightly different implementation because nightly can compile all tests in parallel), and before/after screenshots. I want to be able to run cargo test and observe what you are saying.

[GuillaumeGomez]

I'll write how to reproduce then:

1. Use https://crates.io/crates/trybuild2 (which doesn't include the equivalent fix of this PR that you can see here)
2. Clone https://github.com/gtk-rs/gtk-rs-core locally
3. Go to glib-macros subfolder
4. Run cargo test clone_failures (which you can see here)

On the first run, the tests won't exist (because they need to be generated) and on the first run it'll work. It illustrates what this PR fixes: check_exists is called after the cargo run, making it either useless or too late.

[dtolnay]

That repro doesn't even involve this crate.

I am going to assume this fix is not relevant to this crate.

[GuillaumeGomez]

It is but whatever... Thanks in any case for writing this crate.

[GuillaumeGomez]

For completeness:

1. You run all tests https://github.com/dtolnay/trybuild/blob/master/src/run.rs#L346
2. You check all tests exist (9 lines below) https://github.com/dtolnay/trybuild/blob/master/src/run.rs#L355