Monitoring Specific Messages in RSpec Part 3
Check out the full Monitoring Messages in Rspec series: part 1, part 2, part 3
Continuing the series ( part 1, part 2 ) on matching messages in RSpec, the next logical step is custom argument matchers.
Using the RSpec matcher DSL this could simply look like:
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That’s all there is to it. Now it can be used as both a regular matcher and as an argument matcher.
If the matcher needs to be created from
matches? method must be defined instead:
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This works just fine as a normal matcher, however, when used as an argument
matcher, it will always fail. The reason is that argument matchers are invoked
== operator, which by default,
verifies if the objects are the same object.
Attempting to use a normal matcher with the
oddly fails, due to
change invoking the
matches?. Since the default
=== behavior is
==, the existing
argument matchers currently work with it.
There is active talk / changes
standardize the matchers to
===. This will allow for a more consistent and
composable interface. It also has the added benefit of allowing the matchers to
be used in more complex conditionals using
To fix the class based matcher simply add the necessary alias(es):
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Note that with such a simple matcher, there is no reason it cannot be created as a simple composed method using an existing matcher:
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