Raise an error when given a block with a 0 element assertion

[joshuay03]

Actioning this comment.

I didn't end up opening an issue just for this, please let me know if I should!

[tomhughes]

Is this really reasonable? We have a number of places where we use helper functions that contain code like this one:

assert_select "item", :count => traces.length do |items|
  traces.zip(items).each do |trace, item|
    assert_select item, "title", trace.name
    ...
  end
end

That helper is called from various tests and may be given an empty list of traces or a list that has some entries and until now it has worked fine - if the set is empty then the top level assert looks for zero matches otherwise it checks there are the right number of matches and calls the block to validate them.

[joshuay03]

@tomhughes I did not consider a mixed case like that...

The intention behind the change was to catch unintentional zero counts, for example:

expected_count = org.users.count # unintentionally 0 due to invalid setup
assert_select "user", count: expected_count do |users|
  # assertions that never run but seem like they're valid
  assert_equal "Josh", users.last.text
end

Although I'll admit I can see the usefulness in your case as well. I'll leave it to @rafaelfranca and @flavorjones to make the call on whether this change should be reverted.

If that doesn't happen, your helpers could be refactored to something like:

items = assert_select "item", :count => traces.length
if traces.length.positive?
  traces.zip(items).each do |trace, item|
    assert_select item, "title", trace.name
    ...
  end
end