adding better error reporting for bin tests

[cdleu430]

Adding the stdout or stderr to the AssertionErrors in our tests.

I imagine there are a couple of ways to accomplish this. This seemed like the least intrusive, but it still is a large amount of lines changed, oh well. Happy to take a different approach if others think it would look better, this is my first PR here

Issue:
#1558

Testing:
If you want to test this out yourself it's a bit tricky because you need the tests to fail (which I obviously don't want to do in my commit).
I found changing something like latlong_image value in test_exrenvmap.py was enough to get the test to fail and see what the output looks like.
You can run a single test like:
make test ARGS="-R 'exrenvmap' --output-on-failure"
you need to be in your _build dir to run that

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[lgritz]

I'm not a very fluent Python speaker. What does this mean

assert(condition), string

?? Does the string print if the assertion fails? What about if the assertion succeeds? Is this an idiomatic usage that Python experts would use?

[cdleu430]

Yeah basically it's just passing that string to the Exception. Same as if you did
Exception("This is my error message")
https://docs.python.org/3.9/reference/simple_stmts.html#the-assert-statement
I'm using "the extended form" here

So the string only prints if the assertion fails.

I think an alternative would be

try:
    assert(result.returncode != 0)
except AssertionError:
    print(result.stderr)
    raise

But that just felt like it took up too many lines for what it did.

[lgritz]

No, it's fine, it just wasn't a convention I was familiar with

[cary-ilm]

Nice, succinct solution, thanks!