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Extended equality

marick edited this page Mar 1, 2013 · 4 revisions

Midje checks the right-hand side of a checkable's=> using extended equality. That adds some special cases onto Clojure's =:

  • Functions: When the right-hand-side is a function, it's applied to the actual result:

         1 => even?

    See Checkers for a prepackaged set of useful functions.

  • Regular expressions: When the left-hand-side is a string and the right-hand-side is a regular expression, the behavior is that of re-find:

         "the entire string need not match" => #"ne*d"

    If you want the entire string to match, you can either write the regular expression with ^ and $, or you can use one of the prepackaged collection checkers:

         "the entire string need not match" => (just #"ne*d")  ; fails

    Unlike with Clojure's equality, two regular expressions formed from = strings are counted as equal.

  • Maps and records: "Classic" maps can be compared to records. Using a record on the right-hand side means you want the left-hand side's value to have the same type as well as the same key-value pairs. Using a map means you care only about key-value pairs. Examples:

        (defrecord AB [a b])
        (fact (AB. 1 2) => (AB. 1 2))     ; true
        (fact {:a 1, :b 2} => (AB. 1 2))  ; false, as with normal Clojure equality
        (fact (AB. 1 2) => {:a 1, :b 2})  ; true: all that matters is keys and values.
  • Exceptions: If a comparison would normally blow up, it returns false:

        "five" => odd? ; false instead of a java.lang.ClassCastException
  • Collections: The collection checkers can be used to apply extended equality to each collection element. The following example insists a collection be exactly two even numbers followed by two odd:

        [2 4 1 3] => (just [even? even? odd? odd?])
  • Direct access: If you want to use extended equality in your own checkers, include this in your namespace declaration:

        (:use [midje.checking.core :only [extended-=]])
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