```ruby

require_relative '../lib/message_filter'

describe MessageFilter, 'with argument "foo"' do
  subject { MessageFilter.new('foo') }
  it { is_expected.to be_detect('hello from foo') }
  it { is_expected.not_to be_detect('hello, world!') }
end

describe MessageFilter, 'with argument "foo","bar"' do
  subject { MessageFilter.new('foo', 'bar') }
  it { is_expected.to be_detect('hello from bar') }
end
```

Add specs for variable length argument
user
```ruby

require_relative '../lib/message_filter'

describe MessageFilter, 'with argument "foo"' do
  subject { MessageFilter.new('foo') }
  it { is_expected.to be_detect('hello from foo') }
  it { is_expected.not_to be_detect('hello, world!') }
end

describe MessageFilter, 'with argument "foo","bar"' do
  subject { MessageFilter.new('foo', 'bar') }
  it { is_expected.to be_detect('hello from bar') }
  it { is_expected.to be_detect('hello from foo') }
  it { is_expected.not_to be_detect('hello, world!') }
end
```
assistant