require 'delegate'

class Bar < SimpleDelegator
  def initialize(obj)
    super(obj)
  end
end

class Foo
end

require 'minitest/autorun'

describe Bar do
  subject { Bar.new(Foo.new) }

  it "assert kind of Bar" do
    assert_kind_of(Bar, subject)
  end

  it "must be kind of Bar" do
    subject.must_be_kind_of Bar
  end

  it "assert instance of Bar" do
    assert_instance_of(Bar, subject)
  end

  it "must be instance of Bar" do
    subject.must_be_instance_of Bar
  end
end

➜  ~  /usr/bin/ruby mini.rb
Run options: --seed 24089

# Running:

F.F.

Finished in 0.004433s, 902.2708 runs/s, 902.2708 assertions/s.

  1) Failure:
Bar#test_0004_must be instance of Bar [mini.rb:30]:
Expected #<Foo:0x00000002f49320> to be an instance of Bar, not Foo.


  2) Failure:
Bar#test_0002_must be kind of Bar [mini.rb:22]:
Expected #<Foo:0x00000002f3ee20> to be a kind of Bar, not Foo.

4 runs, 4 assertions, 2 failures, 0 errors, 0 skips