Class: RuboCop::Cop::RSpec::LeakyConstantDeclaration

Inherits:
Base
  • Object
show all
Defined in:
lib/rubocop/cop/rspec/leaky_constant_declaration.rb

Overview

Checks that no class, module, or constant is declared.

Constants, including classes and modules, when declared in a block scope, are defined in global namespace, and leak between examples.

If several examples may define a `DummyClass`, instead of being a blank slate class as it will be in the first example, subsequent examples will be reopening it and modifying its behaviour in unpredictable ways. Even worse when a class that exists in the codebase is reopened.

Anonymous classes are fine, since they don't result in global namespace name clashes.

Examples:

Constants leak between examples

# bad
describe SomeClass do
  OtherClass = Struct.new
  CONSTANT_HERE = 'I leak into global namespace'
end

# good
describe SomeClass do
  before do
    stub_const('OtherClass', Struct.new)
    stub_const('CONSTANT_HERE', 'I only exist during this example')
  end
end
# bad
describe SomeClass do
  class FooClass < described_class
    def double_that
      some_base_method * 2
    end
  end

  it { expect(FooClass.new.double_that).to eq(4) }
end

# good - anonymous class, no constant needs to be defined
describe SomeClass do
  let(:foo_class) do
    Class.new(described_class) do
      def double_that
        some_base_method * 2
      end
    end
  end

  it { expect(foo_class.new.double_that).to eq(4) }
end

# good - constant is stubbed
describe SomeClass do
  before do
    foo_class = Class.new(described_class) do
                  def do_something
                  end
                end
    stub_const('FooClass', foo_class)
  end

  it { expect(FooClass.new.double_that).to eq(4) }
end
# bad
describe SomeClass do
  module SomeModule
    class SomeClass
      def do_something
      end
    end
  end
end

# good
describe SomeClass do
  before do
    foo_class = Class.new(described_class) do
                  def do_something
                  end
                end
    stub_const('SomeModule::SomeClass', foo_class)
  end
end

See Also:

Constant Summary collapse

MSG_CONST =
'Stub constant instead of declaring explicitly.'
MSG_CLASS =
'Stub class constant instead of declaring explicitly.'
MSG_MODULE =
'Stub module constant instead of declaring explicitly.'

Instance Method Summary collapse

Methods inherited from Base

inherited, #on_new_investigation

Methods included from RSpec::Language::NodePattern

#block_pattern, #send_pattern

Instance Method Details

#on_casgn(node) ⇒ Object


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# File 'lib/rubocop/cop/rspec/leaky_constant_declaration.rb', line 101

def on_casgn(node)
  return unless inside_describe_block?(node)

  add_offense(node, message: MSG_CONST)
end

#on_class(node) ⇒ Object


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# File 'lib/rubocop/cop/rspec/leaky_constant_declaration.rb', line 107

def on_class(node)
  return unless inside_describe_block?(node)

  add_offense(node, message: MSG_CLASS)
end

#on_module(node) ⇒ Object


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# File 'lib/rubocop/cop/rspec/leaky_constant_declaration.rb', line 113

def on_module(node)
  return unless inside_describe_block?(node)

  add_offense(node, message: MSG_MODULE)
end