Ruby's Test::Unit
has assert_nothing_raised
. Test::Unit
has been replaced by MiniTest. Why don't MiniTest's assertions / expectations have anything parallel to this? For example you can expect must_raise
but not wont_raise
.
To run a Minitest test, the only setup you really need is to require the autorun file at the beginning of a test file: require 'minitest/autorun' . This is good if you'd like to keep the code small. A better way to get started with Minitest is to have Bundler create a template project for you.
Minitest is a testing tool for Ruby that provides a complete suite of testing facilities. It also supports behaviour-driven development, mocking and benchmarking. With the release of Ruby 1.9, it was added to Ruby's standard library, which increased its popularity.
MiniTest does implement assert_nothing_raised
in its Test::Unit compatibility layer, but in its own tests (MiniTest::Unit
and MiniTest::Spec
) it does not implement any test like this. The reason is, the programmer argues, that testing for nothing raised is not a test of anything; you never expect anything to be raised in a test, except when you are testing for an exception. If an unexpected (uncaught) exception occurs in the code for a test, you'll get an exception reported in good order by the test and you'll know you have a problem.
Example:
require 'minitest/autorun'
describe "something" do
it "does something" do
Ooops
end
end
Output:
Run options: --seed 41521
# Running tests:
E
Finished tests in 0.000729s, 1371.7421 tests/s, 0.0000 assertions/s.
1) Error:
test_0001_does_something(something):
NameError: uninitialized constant Ooops
untitled:5:in `block (2 levels) in <main>'
1 tests, 0 assertions, 0 failures, 1 errors, 0 skips
Which is exactly what you wanted to know. If you were expecting nothing to be raised, you didn't get it and you've been told so.
So, the argument here is: do not use assert_nothing_raised
! It's just a meaningless crutch. See, for example:
https://github.com/seattlerb/minitest/issues/70
https://github.com/seattlerb/minitest/issues/159
http://blog.zenspider.com/blog/2012/01/assert_nothing_tested.html
On the other hand, clearly assert_nothing_raised
corresponds to some intuition among users, since so many people expect a wont_raise
to go with must_raise
, etc. In particular one would like to focus an assertion on this, not merely a test. Luckily, MiniTest is extremely minimalist and flexible, so if you want to add your own routine, you can. So you can write a method that tests for no exception and returns a known outcome if there is no exception, and now you can assert for that known outcome.
For example (I'm not saying this is perfect, just showing the idea):
class TestMyRequire < MiniTest::Spec
def testForError # pass me a block and I'll tell you if it raised
yield
"ok"
rescue
$!
end
it "blends" do
testForError do
something_or_other
end.must_equal "ok"
end
end
The point is not that this is a good or bad idea but that it was never the responsibility of MiniTest to do it for you.
If you need it:
# test_helper.rb
module Minitest::Assertions
def assert_nothing_raised(*)
yield
end
end
And to use it:
def test_unknown_setter
assert_nothing_raised do
result.some_silly_column_name = 'value'
end
end
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