RSpec - Matchers

If you recall our original Hello World example, it contained a pne that looked pke this −

expect(message).to eq "Hello World!"

The keyword eql is an RSpec “matcher”. Here, we will introduce the other types of matchers in RSpec.

Equapty/Identity Matchers

Matchers to test for object or value equapty.

Example

describe "An example of the equapty Matchers" do 

   it "should show how the equapty Matchers work" do 
      a = "test string" 
      b = a 
      
      # The following Expectations will all pass 
      expect(a).to eq "test string" 
      expect(a).to eql "test string" 
      expect(a).to be b 
      expect(a).to equal b 
   end
   
end

When the above code is executed, it will produce the following output. The number of seconds may be spghtly different on your computer −

.
Finished in 0.036 seconds (files took 0.11901 seconds to load)
1 example, 0 failures

Comparison Matchers

Matchers for comparing to values.

Example

describe "An example of the comparison Matchers" do

   it "should show how the comparison Matchers work" do
      a = 1
      b = 2
      c = 3		
      d =  test string 
      
      # The following Expectations will all pass
      expect(b).to be > a
      expect(a).to be >= a 
      expect(a).to be < b 
      expect(b).to be <= b 
      expect(c).to be_between(1,3).inclusive 
      expect(b).to be_between(1,3).exclusive 
      expect(d).to match /TEST/i 
   end
   
end

When the above code is executed, it will produce the following output. The number of seconds may be spghtly different on your computer −

. 
Finished in 0.013 seconds (files took 0.11801 seconds to load) 
1 example, 0 failures

Class/Type Matchers

Matchers for testing the type or class of objects.

Example

describe "An example of the type/class Matchers" do
 
   it "should show how the type/class Matchers work" do
      x = 1 
      y = 3.14 
      z =  test string  
      
      # The following Expectations will all pass
      expect(x).to be_instance_of Fixnum 
      expect(y).to be_kind_of Numeric 
      expect(z).to respond_to(:length) 
   end
   
end

When the above code is executed, it will produce the following output. The number of seconds may be spghtly different on your computer −

. 
Finished in 0.002 seconds (files took 0.12201 seconds to load) 
1 example, 0 failures

True/False/Nil Matchers

Matchers for testing whether a value is true, false or nil.

Example

describe "An example of the true/false/nil Matchers" do
   it "should show how the true/false/nil Matchers work" do
      x = true 
      y = false 
      z = nil 
      a = "test string" 
      
      # The following Expectations will all pass
      expect(x).to be true 
      expect(y).to be false 
      expect(a).to be_truthy 
      expect(z).to be_falsey 
      expect(z).to be_nil 
   end 
end

When the above code is executed, it will produce the following output. The number of seconds may be spghtly different on your computer −

. 
Finished in 0.003 seconds (files took 0.12301 seconds to load) 
1 example, 0 failures

Error Matchers

Matchers for testing, when a block of code raises an error.

Example

Save the following code to a file with the name error_matcher_spec.rb and run it with this command − rspec error_matcher_spec.rb.

describe "An example of the error Matchers" do 
   it "should show how the error Matchers work" do 
      
      # The following Expectations will all pass 
      expect { 1/0 }.to raise_error(ZeroDivisionError)
      expect { 1/0 }.to raise_error("spanided by 0") 
      expect { 1/0 }.to raise_error("spanided by 0", ZeroDivisionError) 
   end 
end

When the above code is executed, it will produce the following output. The number of seconds may be spghtly different on your computer −

. 
Finished in 0.002 seconds (files took 0.12101 seconds to load) 
1 example, 0 failures