Add specs for bundle lock
user
```ruby
require "spec_helper"

describe "bundle lock" do
  def strip_lockfile(lockfile)
    strip_whitespace(lockfile).sub(/\n\Z/, '')
  end

  def read_lockfile(file = "Gemfile.lock")
    strip_lockfile bundled_app(file).read
  end

  before :each do
    gemfile <<-G
      source "file://#{gem_repo1}"
      gem "rails"
      gem "with_license"
      gem "foo"
    G

    @lockfile = strip_lockfile <<-L
      GEM
        remote: file:#{gem_repo1}/
        specs:
          actionmailer (2.3.2)
            activesupport (= 2.3.2)
          actionpack (2.3.2)
            activesupport (= 2.3.2)
          activerecord (2.3.2)
            activesupport (= 2.3.2)
          activeresource (2.3.2)
            activesupport (= 2.3.2)
          activesupport (2.3.2)
          foo (1.0)
          rails (2.3.2)
            actionmailer (= 2.3.2)
            actionpack (= 2.3.2)
            activerecord (= 2.3.2)
            activeresource (= 2.3.2)
            rake (= 10.0.2)
          rake (10.0.2)
          with_license (1.0)

      PLATFORMS
        ruby

      DEPENDENCIES
        foo
        rails
        with_license
    L
  end

  it "prints a lockfile when there is no existing lockfile with --print" do
    bundle "lock --print"

    expect(out).to eq(@lockfile)
  end

  it "prints a lockfile when there is an existing lockfile with --print" do
    lockfile @lockfile

    bundle "lock --print"

    expect(out).to eq(@lockfile)
  end

  it "writes a lockfile when there is no existing lockfile" do
    bundle "lock"

    expect(read_lockfile).to eq(@lockfile)
  end

  it "writes a lockfile when there is an outdated lockfile using --update" do
    lockfile @lockfile.gsub('2.3.2', '2.3.1')

    bundle "lock --update"

    expect(read_lockfile).to eq(@lockfile)
  end

  it "does not fetch remote specs when using the --local option" do
    bundle "lock --update --local"

    expect(out).to include("in the gems available on this machine.")
  end

  it "writes to a custom location using --lockfile" do
    bundle "lock --lockfile=lock"

    expect(out).to match(/Writing lockfile to.+lock/)
    expect(read_lockfile "lock").to eq(@lockfile)
    expect { read_lockfile }.to raise_error
  end
end
```
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