Add Integer.try_convert [Feature #15211]

Merged: https://github.com/ruby/ruby/pull/4654

spec/ruby/core/integer/try_convert_spec.rb

@@ -0,0 +1,40 @@
+require_relative '../../spec_helper'
+require_relative 'fixtures/classes'
+
+ruby_version_is "3.1" do
+  describe "Integer.try_convert" do
+    it "returns the argument if it's an Integer" do
+      x = 42
+      Integer.try_convert(x).should equal(x)
+    end
+
+    it "returns nil when the argument does not respond to #to_int" do
+      Integer.try_convert(Object.new).should be_nil
+    end
+
+    it "sends #to_int to the argument and returns the result if it's nil" do
+      obj = mock("to_int")
+      obj.should_receive(:to_int).and_return(nil)
+      Integer.try_convert(obj).should be_nil
+    end
+
+    it "sends #to_int to the argument and returns the result if it's an Integer" do
+      x = 234
+      obj = mock("to_int")
+      obj.should_receive(:to_int).and_return(x)
+      Integer.try_convert(obj).should equal(x)
+    end
+
+    it "sends #to_int to the argument and raises TypeError if it's not a kind of Integer" do
+      obj = mock("to_int")
+      obj.should_receive(:to_int).and_return(Object.new)
+      -> { Integer.try_convert obj }.should raise_error(TypeError)
+    end
+
+    it "does not rescue exceptions raised by #to_int" do
+      obj = mock("to_int")
+      obj.should_receive(:to_int).and_raise(RuntimeError)
+      -> { Integer.try_convert obj }.should raise_error(RuntimeError)
+    end
+  end
+end