Recently I was taking a look at my tests and noticed some things. I’ve been writing tests for my tests without knowing it.
Here’s one I commonly do when testing the ordering of results from an
ActiveRecord class side finder.
This is wrong:
def test_should_find_all_posts_ordered_by_most_recent_first_when_sent_recent
posts = Post.recent
posts.each_with_index do |each, index|
if posts[index.succ]
assert each.created_on >= posts[index.succ].created_on
end
end
end
The problem with this test is that Post#recent could return an empty Array,
then #each_with_index would not run and no assertions would be run but the
test would still pass.
Rewrite:
def test_should_find_all_posts_ordered_by_most_recent_first_when_sent_recent
posts = Post.recent
assert ! posts.empty?
posts.each_with_index do |each, index|
if posts[index.succ]
assert each.created_on >= posts[index.succ].created_on
end
end
end
Better.
Now we #assert that the collection returned from Post#recent is at least not
#empty? However this test can still pass without executing 1 assertion
because in order to test ordering you need at least 2 objects.
Rewrite:
def test_should_find_all_posts_ordered_by_most_recent_first_when_sent_recent
posts = Post.recent
assert ! posts.empty?
assert posts.size >= 2
posts.each_with_index do |each, index|
if posts[index.succ]
assert each.created_on >= posts[index.succ].created_on
end
end
end
Now its good.
There’s no way this test will pass without testing that the collection of
posts found by Post#recent is ordered by most recent first.
