Pattern: Leaky constant declaration
Issue: -
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.
Anonymous classes are fine, since they don't result in global namespace name clashes.
# 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