Using RSpec to check if something is an instance of another object

Question

I need a way to check if an object is an instance of another object using RSpec. For example:

describe "new shirt" do
  it "should be an instance of a Shirt object"
    # How can i check if it is an instance of a shirt object
  end
end

Note that an object is never an "instance of another object." An object is an instance of a class, not another object. — Jacob Lockard
– Jacob Lockard, Commented Jul 15, 2020 at 0:09
@JacobLockard Classes are objects in Ruby. The Ruby documentation states: "Classes in Ruby are first-class objects—each is an instance of class Class." and "When a new class is created, an object of type Class is initialized and assigned to a global constant." ruby-doc.org/core-2.5.3/Class.html — Dillon Benson
– Dillon Benson, Commented Jul 23, 2020 at 22:47

doppelgreener · Accepted Answer · 2015-01-20 23:42:05Z

165

The preferred syntax is:

expect(@object).to be_a Shirt

The older syntax is:

@object.should be_an_instance_of Shirt

Note that there is a very subtle difference between the two. If Shirt were to inherit from Garment then both of these expectations will pass:

expect(@object).to be_a Shirt
expect(@object).to be_a Garment

If you do and @object is a Shirt, then the second expectation will fail:

@object.should be_an_instance_of Shirt
@object.should be_an_instance_of Garment

doppelgreener

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answered Dec 20, 2012 at 4:19

Dillon Benson

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Comments

Chris Salzberg · Accepted Answer · 2012-11-25 04:59:16Z

8

You mean you want to check if an object is an instance of a class? If so, that's easy, just use class:

@object.class.should == Shirt

answered Nov 25, 2012 at 4:59

Chris Salzberg

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