In Ruby unit tests, how to assert that a string contains certain substring?

You could go with assert_match pattern, string, [message] which is true if string =~ pattern:

assert_match substring_to_verify, string_to_test

e.g.

assert_match /foo/, "foobar"

If you use this very often, why not write your own assertion?

require 'test/unit'module Test::Unit::Assertions  def assert_contains(expected_substring, string, *args)    assert_match expected_substring, string, *args  endend

Alternatively, using the method described by @IvayloStrandjev (way easier to understand), you could define

require 'test/unit'module Test::Unit::Assertions  def assert_contains(expected_substring, string, *args)    assert string.include?(expected_substring), *args  endend

The usage is exactly as you requested in your question, e.g.

class TestSimpleNumber < Test::Unit::TestCase  def test_something    assert_contains 'foo', 'foobar'  end  def test_something_fails    assert_contains 'x', 'foobar', 'Does not contain x'  endend

Which will produce

Run options:# Running tests:.FFinished tests in 0.000815s, 2453.9877 tests/s, 2453.9877 assertions/s.  1) Failure:test_something_fails(TestSimpleNumber) [assertion.rb:15]:Does not contain x2 tests, 2 assertions, 1 failures, 0 errors, 0 skips

Edit

As requested, with automated message:

module Test::Unit::Assertions  def assert_contains(exp_substr, obj, msg=nil)    msg = message(msg) { "Expected #{mu_pp obj} to contain #{mu_pp exp_substr}" }    assert_respond_to obj, :include?    assert obj.include?(exp_substr), msg  endend

adapted from the original assert_match source. This actually also works with Arrays!

assert_contains 3, [1,2,3]

You can write assert string_to_test.include?(string_to_verify) for instance. You can not expect to have asserts for all the checks you would like to perform, so just go the the classic check of a boolean condition.

Also have a look here to see a list of all available assertions.

There is assert_includes:

assert_includes 'foobar', 'foo'

will assert that foobar contains foo.