Avoid hiding assertion failures in teardown.

We don’t need to use a generalized `eventually` which listens for assertion errors in teardown, as we know what we are waiting for.

spec/promises_aplus.rb

@@ -4,26 +4,18 @@ def setup
   end
 
   def teardown
-    eventually { @done.must_equal true }
-  end
-
-  def done!
-    @done = true
-  end
-
-  def eventually(&block)
     time_limit = Time.now + 2
     loop do
-      begin
-        yield
-      rescue Minitest::Assertion => error
-      end
-      return if error.nil?
-      raise error if Time.now >= time_limit
+      return if @done == true
+      raise Minitest::Assertion.new("`done` was never called") if Time.now >= time_limit
       sleep 0.05
     end
   end
 
+  def done!
+    @done = true
+  end
+
   def self.test_fulfilled(base, value, &test)
     base.it "already-fulfilled" do
       test.call(resolved(value), method(:done!))