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Project: RSpec Expectations 2.7

Publisher: RSpec

raise_error matcher

Use the raise_error matcher to specify that a block of code raises an
error. The most basic form passes if any error is thrown:

expect { raise StandardError }.to raise_error

You can use raise_exception instead if you prefer that wording:

expect { 3 / 0 }.to raise_exception

raise_error and raise_exception are functionally interchangeable, so use
the one that makes the most sense to you in any given context.

In addition to the basic form, above, there are a number of ways to specify
details of an error/exception:

expect { raise "oops" }.to raise_error
expect { raise "oops" }.to raise_error(RuntimeError)
expect { raise "oops" }.to raise_error("oops")
expect { raise "oops" }.to raise_error(/op/)
expect { raise "oops" }.to raise_error(RuntimeError, "oops")
expect { raise "oops" }.to raise_error(RuntimeError, /op/)
Scenarios
  1. expect any error
  2. expect specific error
  3. match message with a string
  4. match message with a regexp
  5. match type + message with string
  6. match type + message with regexp
  7. set expectations on error object passed to block
  8. expect no occurence of a specific error
  9. expect no error at all
expect any error
Given
a file named "example_spec" with: 
describe "calling a missing method" do
  it "raises" do
    expect { Object.new.foo }.to raise_error
  end
end
When
I run rspec example_spec
Then
the example should pass
expect specific error
Given
a file named "example_spec" with: 
describe "calling a missing method" do
  it "raises" do
    expect { Object.new.foo }.to raise_error(NameError)
  end
end
When
I run rspec example_spec
Then
the example should pass
match message with a string
Given
a file named "example_spec.rb" with: 
describe "matching error message with string" do
  it "matches the error message" do
    expect { raise StandardError, 'this message exactly'}.
      to raise_error('this message exactly')
  end
end
When
I run rspec example_spec.rb
Then
the example should pass
match message with a regexp
Given
a file named "example_spec.rb" with: 
describe "matching error message with regex" do
  it "matches the error message" do
    expect { raise StandardError, "my message" }.
      to raise_error(/my mess/)
  end
end
When
I run rspec example_spec.rb
Then
the example should pass
match type + message with string
Given
a file named "example_spec.rb" with: 
describe "matching error message with string" do
  it "matches the error message" do
    expect { raise StandardError, 'this message exactly'}.
      to raise_error(StandardError, 'this message exactly')
  end
end
When
I run rspec example_spec.rb
Then
the example should pass
match type + message with regexp
Given
a file named "example_spec.rb" with: 
describe "matching error message with regex" do
  it "matches the error message" do
    expect { raise StandardError, "my message" }.
      to raise_error(StandardError, /my mess/)
  end
end
When
I run rspec example_spec.rb
Then
the example should pass
set expectations on error object passed to block
Given
a file named "example_spec" with: 
describe "#foo" do
  it "raises NameError" do
    expect { Object.new.foo }.to raise_error { |error|
      error.should be_a(NameError)
    }
  end
end
When
I run rspec example_spec
Then
the example should pass
expect no occurence of a specific error
Given
a file named "example_spec" with: 
describe Object, "#public_instance_methods" do
  it "does not raise" do
    expect { Object.public_instance_methods }.
      to_not raise_error(NameError)
  end
end
When
I run rspec example_spec
Then
the example should pass
expect no error at all
Given
a file named "example_spec" with: 
describe "#to_s" do
  it "does not raise" do
    expect { Object.new.to_s }.to_not raise_error
  end
end
When
I run rspec example_spec
Then
the example should pass

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