Add spec for TracePoint.allow_reentry - https://bugs.ruby-lang.org/is…

…sues/15912

core/tracepoint/allow_reentry_spec.rb

@@ -0,0 +1,32 @@
+require_relative '../../spec_helper'
+require_relative 'fixtures/classes'
+
+ruby_version_is "3.1" do
+  describe 'TracePoint.allow_reentry' do
+    it 'allows the reentrance in a given block' do
+      event_lines = []
+      l1 = l2 = l3 = l4 = nil
+      TracePoint.new(:line) do |tp|
+        next unless TracePointSpec.target_thread?
+
+        event_lines << tp.lineno
+        next if (__LINE__ + 2 .. __LINE__ + 4).cover?(tp.lineno)
+        TracePoint.allow_reentry do
+          a = 1; l3 = __LINE__
+          b = 2; l4 = __LINE__
+        end
+      end.enable do
+        c = 3; l1 = __LINE__
+        d = 4; l2 = __LINE__
+      end
+
+      event_lines.should == [l1, l3, l4, l2, l3, l4]
+    end
+
+    it 'raises RuntimeError' do
+      -> {
+        TracePoint.allow_reentry{}
+      }.should raise_error(RuntimeError)
+    end
+  end
+end