Expect.equal throws an NRE on failure

[isaacabraham]

On Expecto 8.10.1, the following code in an F# script fails with an NRE rather than a "pretty" error.

open Expecto
Expect.equal 1 2 "Doh!"

with the error:

System.NullReferenceException: Object reference not set to an instance of an object.
   at Expecto.Expect.highlightAllGreen(FSharpList`1 diffs, String s) in C:\Users\Anthony Lloyd\src\expecto\Expecto\Expect.fs:line 45
   at Expecto.Expect.printVerses[a,b](String firstName, a first, String secondName, b second) in C:\Users\Anthony Lloyd\src\expecto\Expecto\Expect.fs:line 66
   at Expecto.Expect.equal$cont@317[a](a actual, a expected, String message, Object e, Object a, Unit unitVar) in C:\Users\Anthony Lloyd\src\expecto\Expecto\Expect.fs:line 335
   at <StartupCode$FSI_0014>.$FSI_0014.main@()
Stopped due to error

Is this something I'm doing "wrong" - can you not call Expect. functions directly in a script or something?

[isaacabraham]

Seems that this error goes away if you call runTests on some arbitrary set of tests first, which suggests that some shared static state first needs to be set before you can run Expect. functions. Is there a way to avoid this? It's surprising to couple a test runner to individual predicate / test helpers.

[AnthonyLloyd]

It's a colours config that is used in the error messages. I've defaulted to 0 if no config sets it. Will go out soon. Workaround is to runTests on an empty set of tests before any Expect.

[AnthonyLloyd]

@isaacabraham can I just check what you are looking to use this for. Just want to consider the default colours. If it's in another test runner I'm not sure if colours would be useful.

[isaacabraham]

@AnthonyLloyd Yes, I just opened the REPL and wanted to experiment with the testing library behaviours outside the context of the test runner.

[isaacabraham]

@AnthonyLloyd additionally, when running in the context of e.g. azure dev ops, a load of control codes seem to be emitted in the console and get in the way of the real textual output. However, that's a side issue related to colours rather than this NRE.

[isaacabraham]

I suspect that the commit linked above (5a675cb) won't address the root cause e.g. someone running a script on mac or linux will still get this error.

[AnthonyLloyd]

@isaacabraham Need to set --colours 0. They are ANSI control codes. No sensible way of detecting if they are not supported and we default to 8 colours.

[AnthonyLloyd]

I suspect that the commit linked above (5a675cb) won't address the root cause e.g. someone running a script on mac or linux will still get this error.

They'll get the ANSI colour codes.

If you know of any library that handles colour well please let me know. Note we moved from Console commands to ANSI to make it atomic and stop the bug often seen with colour being incorrectly reset.

[haf]

@AnthonyLloyd What would you have against checking whether the terminal is interative? https://github.com/haf/expecto/issues/315#issuecomment-480893080 — if you have a terminal like Travis CI that supports ANSI escape characters, they would be correctly parsed, or if you have Azure, then presumable tty would be false. Would perhaps @isaacabraham be willing to run a script on Azure to test whether this assumption is true?

[isaacabraham]

I think we're conflating the issue here. That was simply about getting an NRE if you call Expecto functions outside of the test runner. Putting a check for Windows won't help that at all I would imagine.

But of course happy to test with dev ops. But sounds like the color argument above will do the trick - I'll try that out

[AnthonyLloyd]

@haf Nothing against it if we can be sure it's a solution. Just wary of complexity that's hard to test.

@isaacabraham sorry, cross issues colours discussion.

[haf]

Putting a check for Windows won't help that at all I would imagine.

No, that's separate; the change that fixed your problem was to default the colours setting to something other than null (None).