diff --git a/core/process/_fork_spec.rb b/core/process/_fork_spec.rb
new file mode 100644
index 0000000000..62e20644ee
--- /dev/null
+++ b/core/process/_fork_spec.rb
@@ -0,0 +1,34 @@
+require_relative '../../spec_helper'
+
+describe "Process._fork" do
+  ruby_version_is ""..."3.1" do
+    it "raises NoMethodError" do
+      -> { Process._fork }.should raise_error(NoMethodError)
+    end
+  end
+
+  ruby_version_is "3.1" do
+    platform_is :windows do
+      it "returns false from #respond_to?" do
+        Process.respond_to?(:_fork).should be_false
+      end
+
+      it "raises a NotImplementedError when called" do
+        -> { Process._fork }.should raise_error(NotImplementedError)
+      end
+    end
+
+    platform_is_not :windows do
+      it "returns true from #respond_to?" do
+        Process.respond_to?(:_fork).should be_true
+      end
+
+      it "is called by Process#fork" do
+        Process.should_receive(:_fork).once.and_return(42)
+
+        pid = Process.fork {}
+        pid.should equal(42)
+      end
+    end
+  end
+end