JSON matcher

Testing RSpec
1

Curiously, there doesn’t seem to be a matcher around that matches a JSON
string against an expected ruby object. Below is what I’ve come up
with, including some Rails idiosyncrasies. Any suggestions for
improvements?

Michael

module Spec
module JSONMatchers
class BeJsonEql
def initialize(expected)
@raw_expected = expected
@expected = decode(expected, ‘expected’)
end

  def matches?(target)
    @raw_target = target
    @target = decode(target, 'target')
    @target == @expected
  end

  def failure_message
    "expected\n#{@raw_target}\n" +
    "to be JSON code equivalent to\n#{@raw_expected}\n" +
    "Difference:\n#{@expected.diff(@target).inspect}"
  end

  def negative_failure_message
    "expected\n#{@raw_target}\n" +
    "to be JSON code different from\n#{@raw_expected}"
  end

  private

  def decode(s, which)
    ActiveSupport::JSON.decode(s)
  rescue ActiveSupport::JSON::ParseError
    raise ArgumentError, "Invalid #{which} JSON string:

#{s.inspect}"
end
end

def be_json_eql(expected)
  BeJsonEql.new(expected)
end

end
end

–
Michael S.
mailto:[email protected]
http://www.schuerig.de/michael/

2

Michael S. wrote:

  def failure_message
    "expected\n#{@raw_target}\n" +
    "to be JSON code equivalent to\n#{@raw_expected}\n" +
    "Difference:\n#{@expected.diff(@target).inspect}"
  end

Nice - this fixes the common problem with assertions on large bulky
variables -
they often leave you squinting, trying to see the line that’s different.

But where did .diff() come from? should I know it’s part of
ActiveSupport::JSON
or something?

3

On Tuesday 07 April 2009, Phlip wrote:

But where did .diff() come from? should I know it’s part of
ActiveSupport::JSON or something?

Hash#diff is part of ActiveSupport and when you look at its code you’ll
probably have to squint.

Michael

–
Michael S.
mailto:[email protected]
http://www.schuerig.de/michael/

4

JSON matcher updated (works with Rspec 1.3.1). Put this in
spec/support/matchers/json_matcher.rb:

Spec::Matchers.define :be_json_eql do | expected |
match do | actual |
@expected = decode(expected, ‘expected’)
@actual = decode(actual, ‘actual’)
@actual == @expected
end

failure_message_for_should do | actual |
“expected\n#{actual}\n” +
“to be JSON code equivalent to\n#{expected}\n” +
“Difference:\n#{@expected.diff(@actual).inspect}”
end

failure_message_for_should_not do | actual |
“expected\n#{actual}\n” +
“to be JSON code different from\n#{expected}”
end

def decode(s, which)
ActiveSupport::JSON.decode(s)
rescue ActiveSupport::JSON::ParseError
raise ArgumentError, “Invalid #{which} JSON string:
#{s.inspect}”
end
end