```ruby
require 'introspection_test_helper'

describe GObjectIntrospection::IRepository do
  describe "an instance" do
    it "is not created by calling new()" do
      assert_raises NoMethodError do
        GObjectIntrospection::IRepository.new
      end
    end

    it "is created by calling default()" do
      gir = GObjectIntrospection::IRepository.default
      assert_kind_of GObjectIntrospection::IRepository, gir
    end

    it "is a singleton" do
      gir = GObjectIntrospection::IRepository.default
      gir2 = GObjectIntrospection::IRepository.default
      assert_equal gir, gir2
    end
  end

  describe "#require" do
    it "raises an error if the namespace doesn't exist" do
      assert_raises RuntimeError do
        GObjectIntrospection::IRepository.default.require 'VeryUnlikelyGObjectNamespaceName', nil
      end
    end

    it "allows version to be nil" do
      GObjectIntrospection::IRepository.default.require 'GObject', nil
      pass
    end

    it "allows version to be left out" do
      GObjectIntrospection::IRepository.default.require 'GObject'
      pass
    end
  end

  describe "enumerating the infos for GObject" do
    before do
      @gir = GObjectIntrospection::IRepository.default
      @gir.require 'GObject', "2.0"
    end

    it "yields more than one object" do
      assert_operator @gir.n_infos('GObject'), :>, 0
    end

    it "yields IBaseInfo objects" do
      assert_kind_of GObjectIntrospection::IBaseInfo, @gir.info('GObject', 0)
    end
  end
end
```

Simplify IRepository tests with a let block
user
```ruby
require 'introspection_test_helper'

describe GObjectIntrospection::IRepository do
  describe "an instance" do
    it "is not created by calling new()" do
      assert_raises NoMethodError do
        GObjectIntrospection::IRepository.new
      end
    end

    it "is created by calling default()" do
      gir = GObjectIntrospection::IRepository.default
      assert_kind_of GObjectIntrospection::IRepository, gir
    end

    it "is a singleton" do
      gir = GObjectIntrospection::IRepository.default
      gir2 = GObjectIntrospection::IRepository.default
      assert_equal gir, gir2
    end
  end

  let(:gir) { GObjectIntrospection::IRepository.default }

  describe "#require" do
    it "raises an error if the namespace doesn't exist" do
      assert_raises RuntimeError do
        gir.require 'VeryUnlikelyGObjectNamespaceName', nil
      end
    end

    it "allows version to be nil" do
      gir.require 'GObject', nil
      pass
    end

    it "allows version to be left out" do
      gir.require 'GObject'
      pass
    end
  end

  describe "enumerating the infos for GObject" do
    before do
      gir.require 'GObject', "2.0"
    end

    it "yields more than one object" do
      assert_operator gir.n_infos('GObject'), :>, 0
    end

    it "yields IBaseInfo objects" do
      assert_kind_of GObjectIntrospection::IBaseInfo, gir.info('GObject', 0)
    end
  end
end
```
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