a.cr

abstract struct A
  def self.build(value)
    if value.nil?
      B.new
    else
      C.new
    end
  end
end

struct B < A
end

struct C < A
end

describe A do
  it "C" do
    result = A.build(42)
    result.should eq(C.new)
  end
  
  it "B" do
    result = A.build(nil)
    result.should eq(B.new)
  end
end

.F

Failures:

  1) A B
     Failure/Error: result.should eq(B.new)

       Expected: B() : B
            got: B() : B

     # spec/a_spec.cr:51

Finished in 887 microseconds
2 examples, 1 failures, 0 errors, 0 pending