ruby - How can I check if my subject raises an exception?

Question

I'm currently creating an object in subject and need to test if this raises an exception. The following code illustrates what I'm trying to achieve:

describe MyClass do
  describe '#initialize' do
    subject { MyClass.new }

    it { is_expected.not_to raise_error(Some::Error) }
  end
end

I have a feeling I'm going about this the wrong way. What is the preferred way to set the subject to a new object, without creating the object twice?

Update

My problem was two-fold. Firstly, this syntax does not work:

it { is_expected.not_to raise_error }

Using expect inside an it block does, however (as pointed out by Jimmy Cuadra):

it 'does not raise an error' do
  expect { subject }.not_to raise_error
end

I am not well enough acquainted with RSpec to tell you why this is.

Secondly, since RSpec 3.0.0.beta1, it is longer possible to use raise_error with a specific error class. The following, therefore, is invalid:

expect { subject }.to raise_error(Some::Error)

For more information, see

score 11 · Accepted Answer

如果我理解正确，您正在尝试测试实例化一个类是否会导致异常。你只需这样做：

describe MyClass do
  it "doesn't raise an exception when instantiated" do
    expect { subject }.not_to raise_error
  end
end

score 6 · Accepted Answer

通过语法做到这一点的正确方法is_expected是用 Proc 包装您的主题值，如下例所示：

describe MyClass do
  describe '#initialize' do
    subject { -> { MyClass.new } }
    it      { is_expected.not_to raise_error(Some::Error) }
  end
end

这种方式更准确，因为有时您的用例是期望不应抛出特定类型的异常（而允许抛出其他异常）。这种方法将涵盖此类用例。

ruby - How can I check if my subject raises an exception?

2 回答 2

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