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Checks that two values are same and "magically" replaces expected value with the actual in case the new behavior (and new actual value) is correct. Support two kind of arguments: string and code block.

This check works with both Test/Unit and RSpec. See documentation and examples below:



Testing String Values

It is better to start with no expected value

assert_value "foo"

Then run tests as usual with "rake test". As a result you will see diff between expected and actual values:

@@ -1,0, +1,1 @@
Accept the new value: yes to all, no to all, yes, no? [Y/N/y/n] (y):

If you accept the new value your test will be automatically modified to

assert_value "foo", <<-END

Testing Block Values

assert_value can take code block as an argument. If executed block raises exception then exception message is returned as actual value:

assert_value do

Run tests

@@ -1,0, +1,1 @@
+Exception NoMethodError: undefined method `+' for nil:NilClass
Accept the new value: yes to all, no to all, yes, no? [Y/N/y/n] (y): 

After the new value is accepted you get

assert_value(<<-END) do
    Exception NoMethodError: undefined method `+' for nil:NilClass
    nil + 1

Testing Values Stored in Files

Sometimes test string is too large to be inlined into the test source. Put it into the file instead:

assert_value "foo", log: 'test/log/reference.txt'

Additional Test/Unit Options:

--no-interactive skips all questions and just reports failures
--autoaccept prints diffs and automatically accepts all new actual values
--no-canonicalize turns off expected and actual value canonicalization (see below for details)

Additional options can be passed during both single test file run and rake test run:

In Ruby 1.8:

ruby test/unit/foo_test.rb -- --autoaccept
rake test TESTOPTS="-- --autoaccept"

In Ruby 1.9:

ruby test/unit/foo_test.rb --autoaccept
rake test TESTOPTS="--autoaccept"


In specs you can either call assert_value directly or use "be_same_value_as" matcher:

describe "spec with be_same_value_as matcher" do
    it "compares with inline value" do
        expect("foo").to be_same_value_as <<-END

    it "compares with inline block" do
        expect { "foo" }.to be_same_value_as <<-END

    it "compares with value in file" do
        expect("foo").to be_same_value_as(:log => 'test/logs/assert_value_with_files.log.ref')


Before comparing expected and actual strings, assert_value canonicalizes both using these rules:

  • indentation is ignored (except for indentation relative to the first line of the expected/actual string)
  • ruby-style comments after "#" are ignored
  • empty lines are ignored
  • trailing whitespaces are ignored

You can turn canonicalization off with --no-canonicalize option. This is useful when you need to regenerate expected test strings. To regenerate the whole test suite, run:

In Ruby 1.8:

rake test TESTOPTS="-- --no-canonicalize --autoaccept"

In Ruby 1.9:

rake test TESTOPTS="--no-canonicalize --autoaccept"

Supported Rubies and Test Frameworks

Framework / Ruby 1.8.7 1.9.3 2.0+
Test-Unit (bundled) Yes No No
Minitest (bundled) No Yes No
Test-Unit (latest) No No Yes
Minitest (latest) No No Yes
Rspec 2.99 Yes Yes No
Rspec (latest) Yes Yes Yes
  • ruby 1,8.7 came with bundled Test-unit 1.2.3 and cannot run latest Test-Unit and Minitest frameworks
  • ruby 1.9.3 came with bundled Minitest 2.5.1 and cannot run other Test-Unit and MInitest frameworks
  • RSpec 2.99 is the latest RSpec framework compatible with Rails 2.3


One way to setup development environment using rbenv:

# compile ruby
rbenv install 2.3.0

# set local version of ruby under rbenv
rbenv local 2.3.0

# install bundler
gem install bundle

# configure bundler
bundle config --local path .bundle/gems
bundle config --local bin .bundle/bin    # binstubs
bundle config   # to see current settings

# below seems to be necessary, having a Gemfile in
# subdirectory like
#    bundle config --local gemfile gemfiles/test-unit.bundled.gemfile
# breaks tests in old rubies
ln -s gemfiles/test-unit.bundled.gemfile Gemfile

# install gems
bundle install

Run Tests

Test-Unit and Minitest

bundle exec rake test

RSpec 2.99

bundle exec rspec test

RSpec 3+

bundle exec rake spec

Building The Gem

gem build assert_value.gemspec
ls assert_value-*.gem
gem push assert_value-*.gem


  • 1.5: Improve support for various testing frameworks and Ruby versions: Ruby 2.2.2, 2.2.3, RSpec 2.x, 3.x, Test::Unit 2.x, 3.x, Minitest 4.x, 5.x
  • 1.4: Fix RSpec support
  • 1.3: Improve support for various testing frameworks, fix assertion counters
  • 1.2: Rails 4.1 and minitest gem support
  • 1.1: RSpec support
  • 1.0: Rename to assert_value
  • 0.7: Support Ruby 1.9's MiniTest
  • 0.6: Support test execution on Mac
  • 0.5: Support code blocks to assert_same
  • 0.4: Added support for code blocks as argument
  • 0.3: Ruby 1.9 is supported
  • 0.2: Make assert_same useful as a standalone gem. Bugfixes
  • 0.1: Initial release