1 files changed, 48 insertions, 4 deletions
diff --git a/spec/ruby/core/kernel/singleton_method_spec.rb b/spec/ruby/core/kernel/singleton_method_spec.rb
index 0bdf125ad8..fe8e23eb02 100644
--- a/spec/ruby/core/kernel/singleton_method_spec.rb
+++ b/spec/ruby/core/kernel/singleton_method_spec.rb
@@ -1,10 +1,10 @@
 require_relative '../../spec_helper'
 
 describe "Kernel#singleton_method" do
-  it "find a method defined on the singleton class" do
+  it "finds a method defined on the singleton class" do
     obj = Object.new
     def obj.foo; end
-    obj.singleton_method(:foo).should be_an_instance_of(Method)
+    obj.singleton_method(:foo).should.instance_of?(Method)
   end
 
   it "returns a Method which can be called" do
@@ -23,7 +23,7 @@ describe "Kernel#singleton_method" do
     obj.foo.should == 42
     -> {
       obj.singleton_method(:foo)
-    }.should raise_error(NameError) { |e|
+    }.should.raise(NameError) { |e|
       # a NameError and not a NoMethodError
       e.class.should == NameError
     }
@@ -33,9 +33,53 @@ describe "Kernel#singleton_method" do
     obj = Object.new
     -> {
       obj.singleton_method(:not_existing)
-    }.should raise_error(NameError) { |e|
+    }.should.raise(NameError) { |e|
       # a NameError and not a NoMethodError
       e.class.should == NameError
     }
   end
+
+  ruby_bug "#20620", ""..."3.4" do
+    it "finds a method defined in a module included in the singleton class" do
+      m = Module.new do
+        def foo
+          :foo
+        end
+      end
+
+      obj = Object.new
+      obj.singleton_class.include(m)
+
+      obj.singleton_method(:foo).should.instance_of?(Method)
+      obj.singleton_method(:foo).call.should == :foo
+    end
+
+    it "finds a method defined in a module prepended in the singleton class" do
+      m = Module.new do
+        def foo
+          :foo
+        end
+      end
+
+      obj = Object.new
+      obj.singleton_class.prepend(m)
+
+      obj.singleton_method(:foo).should.instance_of?(Method)
+      obj.singleton_method(:foo).call.should == :foo
+    end
+
+    it "finds a method defined in a module that an object is extended with" do
+      m = Module.new do
+        def foo
+          :foo
+        end
+      end
+
+      obj = Object.new
+      obj.extend(m)
+
+      obj.singleton_method(:foo).should.instance_of?(Method)
+      obj.singleton_method(:foo).call.should == :foo
+    end
+  end
 end