Java: Test generator improvements

[joefarebrother]

This PR allows the test generator to accept a yml file or a diretory of yml files containing MaD specifications as input.
Also, the generated "return type" of a constuctor is now considered to be the constructed type.

[atorralba]

Thanks for adding this! It'll be super useful for the rest of the modeling work we're doing.

I added some minor comments, but otherwise this LGTM.

[atorralba]

May I suggest an implementation a bit more pythonic?

Suggested change

	specs = []
	for f in os.listdir(dirname):
	if f.endswith('.yml'):
	specs += readYml(f"{dirname}/{f}")
	return specs
	return [readYml(f"{dirname}/{f}") for f in os.listdir(dirname) if f.endswith('.yml')]

[joefarebrother]

That isn't equivalent is it? As that would result in a list of lists, rather than a single list of rows

[atorralba]

D'oh, true, sorry. That would then probably need to be something like:

Suggested change

	specs = []
	for f in os.listdir(dirname):
	if f.endswith('.yml'):
	specs += readYml(f"{dirname}/{f}")
	return specs
	return [row for row in readYml(f"{dirname}/{f}") for f in os.listdir(dirname) if f.endswith('.yml')]

But the readability starts getting bad at that point, so feel free to leave it as it is.