```ruby
require 'spec_helper'

describe Mutant::Isolation::None do
  before do
    @initial = 1
  end

  describe '.run' do
    let(:object) { described_class }

    it 'does not isolate side effects' do
      object.call { @initial = 2 }
      expect(@initial).to be(2)
    end

    it 'return block value' do
      expect(object.call { :foo }).to be(:foo)
    end

  end
end

describe Mutant::Isolation::Fork do
  before do
    @initial = 1
  end

  describe '.run' do
    let(:object) { described_class }

    it 'does isolate side effects' do
      object.call { @initial = 2  }
      expect(@initial).to be(1)
    end

    it 'return block value' do
      expect(object.call { :foo }).to be(:foo)
    end

  end
end
```

Add specification for isolation exception wrapping
user
```ruby
require 'spec_helper'

describe Mutant::Isolation::None do
  before do
    @initial = 1
  end

  describe '.run' do
    let(:object) { described_class }

    it 'does not isolate side effects' do
      object.call { @initial = 2 }
      expect(@initial).to be(2)
    end

    it 'return block value' do
      expect(object.call { :foo }).to be(:foo)
    end

    it 'wraps *all* exceptions' do
      expect { object.call { fail  } }.to raise_error(Mutant::Isolation::Error)
    end

  end
end

describe Mutant::Isolation::Fork do
  before do
    @initial = 1
  end

  describe '.run' do
    let(:object) { described_class }

    it 'does isolate side effects' do
      object.call { @initial = 2  }
      expect(@initial).to be(1)
    end

    it 'return block value' do
      expect(object.call { :foo }).to be(:foo)
    end

    it 'wraps Parallel::DeadWorker exceptions' do
      expect { object.call { fail Parallel::DeadWorker } }.to raise_error(Mutant::Isolation::Error)
    end

  end
end
```
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