# Xmpfilter 0.3.0: automagic Test::Unit assertions and RSpec e

**URL:** <https://www.ruby-forum.com/t/xmpfilter-0-3-0-automagic-test-unit-assertions-and-rspec-e/72318>\
**Category:** Ruby\
**Created:** [October 16, 2006, 12:15pm UTC](https://www.ruby-forum.com/t/xmpfilter-0-3-0-automagic-test-unit-assertions-and-rspec-e/72318 "2006-10-16T12:15:46Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![tulkas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5daacb/32.png) [@tulkas](https://www.ruby-forum.com/u/tulkas)\
**Post date:** [October 16, 2006, 12:15pm UTC](https://www.ruby-forum.com/t/xmpfilter-0-3-0-automagic-test-unit-assertions-and-rspec-e/72318/1 "2006-10-16T12:15:46Z")

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xmpfilter can be obtained from [eigenclass.org](http://eigenclass.org/hiki.rb?xmpfilter)  
xmpfilter.rb can generate RSpec expectations as of 0.3.0 (thank you,  
rubykitch!).

# Overview

xmpfilter.rb is a small tool that can be used to

- generate Test::Unit assertions and RSpec expectations  
semi-automatically
- annotate source code with intermediate results (a bit like irb  
–simple-prompt but only for the lines explicitly marked with # =\>)  
Very useful for example code (such as postings to ruby-talk).

# Usage

xmpfilter.rb takes its input from stdin and writes to stdout. It can run  
in  
several modes (annotation, Test::Unit assertion expansion, RSpec  
expectation  
generation, marker insertion); see  
xmpfilter.rb -h  
README.emacs and README.vim describe how to use xmpfilter.rb from your  
editor.

# Example: code annotation

Just add “# =\>” markers to the lines whose values you want to be shown:

a, b = “foo”, “baz”  
a + b # =\>  
a.size # =\>

will be expanded to (in one keypress in a decent editor, see  
README.emacs and  
README.vim)

a, b = “foo”, “baz”  
a + b # =\> “foobaz”  
a.size # =\> 3

This saves much cut&pasting when you’re posting to ruby-talk/ruby-core  
(I use  
it all the time).

# Example: assertion generation

xmpfilter.rb can generate assertions based on the current behavior of  
the code  
to be tested (iow. the current behavior is assumed to be correct and is  
used  
to generate assertions which won’t be modified by further runs of  
xmpfilter.rb), making it quite useful for regression testing.

Imagine you have a ComplexClass you want to test. You might start with

```
class TestComplexClass < Test::Unit::TestCase
  def setup; @o = ComplexClass.new("foo", false) end
end

```

and then want to add some tests:

def test\_insertion  
@o.insert “bar”  
@o.insert “baz”  
# … assertions here  
end

At this point, you want to add several assertions to verify that the  
values  
returned by @o.size, @o.last, @o.first, @o.complex\_computation and  
@o.last(2)  
are correct. You can just write the following and feed the file to  
xmpfilter.rb in -u mode (the # =\> markers can also be inserted by  
xmpfilter.rb, see README.vim for more information:

def test\_insertion  
@o.insert “bar”  
@o.insert “baz”  
@o.size # =\>  
@o.last # =\>  
@o.first # =\>  
@o.complex\_computation # =\>  
@o.last(2) # =\>  
end

xmpfilter.rb will run the test and remember what happened in each marked  
line,  
and then rewrite the code so that it looks for instance like

def test\_insertion  
@o.insert “bar”  
@o.insert “baz”  
assert\_equal(2, @o.size)  
assert\_equal(“baz”, @o.last)  
assert\_equal(“bar”, @o.first)  
assert\_in\_delta(3.14159265358979, @o.complex\_computation, 0.0001)  
assert\_equal([“baz”, “bar”], @o.last(2))  
end

As you can see, it can save some typing.

You can edit the generated assertions as you want: xmpfilter.rb will not  
modify lines without the “# =\>” marker. xmpfilter.rb can be used  
repeatedly as  
you add more assertions. Imagine you want to verify that @o.last(3)  
raises an  
ArgumentError. You can simply add one line marked with # =\> :

…  
assert\_in\_delta(3.14159265358979, @o.complex\_computation, 0.0001)  
assert\_equal([“baz”, “bar”], @o.last(2))  
@o.last(3) # =\>  
end

and have it expanded by xmpfilter.rb:

…  
assert\_in\_delta(3.14159265358979, @o.complex\_computation, 0.0001)  
assert\_equal([“baz”, “bar”], @o.last(2))  
assert\_raise(ArgumentError){ @o.last(3) }  
end

# Example: RSpec expectations

Here’s some code before and after filtering it with xmpfilter.rb:

```
class X
  Y = Struct.new(:a)
  def foo(b); b ? Y.new(2) : 2 end
  def bar; raise "No good" end
  def baz; nil end
  def fubar(x); x ** 2.0 + 1 end
  def babar; [1,2] end
  A = 1
  A = 1
end

context "Testing xmpfilter's expectation expansion" do
  setup do
@o = X.new
  end

  specify "Should expand should_equal expectations" do
@o.foo(true) # =>
@o.foo(true).a # =>
@o.foo(false) # =>
  end

  specify "Should expand should_raise expectations" do
@o.bar # =>
  end

  specify "Should expand should_be_nil expectations" do
@o.baz # =>
  end

  specify "Should expand correct expectations for complex values" do
@o.babar # =>
  end

  specify "Should expand should_be_close expectations" do
@o.fubar(10) # =>
  end
end

```

after piping it to xmpfilter.rb -s:

```
class X
  Y = Struct.new(:a)
  def foo(b); b ? Y.new(2) : 2 end
  def bar; raise "No good" end
  def baz; nil end
  def fubar(x); x ** 2.0 + 1 end
  def babar; [1,2] end
  A = 1
  A = 1 # !> already initialized constant A
end

context "Testing xmpfilter's expectation expansion" do
  setup do
@o = X.new
  end

  specify "Should expand should_equal expectations" do
(@o.foo(true)).should_be_a_kind_of X::Y
(@o.foo(true).inspect).should_equal "#<struct X::Y a=2>"
(@o.foo(true).a).should_equal 2
(@o.foo(false)).should_equal 2
  end

  specify "Should expand should_raise expectations" do
lambda{(@o.bar)}.should_raise RuntimeError
  end

  specify "Should expand should_be_nil expectations" do
(@o.baz).should_be_nil
  end

  specify "Should expand correct expectations for complex values" do
(@o.babar).should_equal [1, 2]
  end

  specify "Should expand should_be_close expectations" do
(@o.fubar(10)).should_be_close(101.0, 0.0001)
  end
end

```

# License

xmpfilter.rb is licensed under the same terms as Ruby.

---

<div class="post-metadata">

**Author:** ![tulkas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5daacb/32.png) [@tulkas](https://www.ruby-forum.com/u/tulkas)\
**Post date:** [October 16, 2006, 12:23pm UTC](https://www.ruby-forum.com/t/xmpfilter-0-3-0-automagic-test-unit-assertions-and-rspec-e/72318/2 "2006-10-16T12:23:48Z")

</div>

[[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)] On Behalf Of Mauricio F.

# Subject: [ANN] xmpfilter 0.3.0: automagic Test::Unit

# assertions and RSpec expectations

uber cool. are you a god? 🙂  
thanks for sharing xmpfilter.  
kind regards -botp