diff --git a/core/set/classify_spec.rb b/core/set/classify_spec.rb
index a225ab7cb..1cfacf357 100644
--- a/core/set/classify_spec.rb
+++ b/core/set/classify_spec.rb
@@ -23,4 +23,10 @@
     classified = @set.classify { |x| x.length }
     classified.should == { 3 => Set["one", "two"], 4 => Set["four"], 5 => Set["three"] }
   end
+
+  it "does not retain compare_by_identity flag" do
+    set = Set["one", "two"].compare_by_identity
+    classified = set.classify { |x| x.length }
+    classified.values.each { |s| s.compare_by_identity?.should == false }
+  end
 end
diff --git a/core/set/divide_spec.rb b/core/set/divide_spec.rb
index 409a22df7..e00e4616e 100644
--- a/core/set/divide_spec.rb
+++ b/core/set/divide_spec.rb
@@ -17,6 +17,12 @@
     ret.should.is_a?(Enumerator)
     ret.each(&:even?).should == Set[Set[1, 3], Set[2, 4]]
   end
+
+  it "does not retain compare_by_identity flag" do
+    set = Set["one", "two"].compare_by_identity
+    res = set.divide { |x| x.length }
+    res.each { |s| s.compare_by_identity?.should == false }
+  end
 end
 
 describe "Set#divide when passed a block with an arity of 2" do
diff --git a/core/set/exclusion_spec.rb b/core/set/exclusion_spec.rb
index 52ee34fe7..5457e6e3d 100644
--- a/core/set/exclusion_spec.rb
+++ b/core/set/exclusion_spec.rb
@@ -14,4 +14,19 @@
     -> { @set ^ 3 }.should.raise(ArgumentError)
     -> { @set ^ Object.new }.should.raise(ArgumentError)
   end
+
+  ruby_version_is ""..."4.0" do
+    it "does not retain compare_by_identity flag" do
+      @set.compare_by_identity
+      (@set ^ Set[3, 4, 5]).compare_by_identity?.should == false
+      (@set ^ [3, 4, 5]).compare_by_identity?.should == false
+    end
+  end
+  ruby_version_is "4.0" do
+    it "retains compare_by_identity flag" do
+      @set.compare_by_identity
+      (@set ^ Set[3, 4, 5]).compare_by_identity?.should == true
+      (@set ^ [3, 4, 5]).compare_by_identity?.should == true
+    end
+  end
 end
diff --git a/core/set/flatten_spec.rb b/core/set/flatten_spec.rb
index ca6323fac..65c63a9b7 100644
--- a/core/set/flatten_spec.rb
+++ b/core/set/flatten_spec.rb
@@ -23,6 +23,11 @@
       end
     end
   end
+
+  it "does not retain compare_by_identity flag" do
+    set = Set[1, 2, Set[3, 4]].compare_by_identity
+    set.flatten.compare_by_identity?.should == false
+  end
 end
 
 describe "Set#flatten!" do
@@ -46,4 +51,16 @@
     (set = Set[]) << set
     -> { set.flatten! }.should.raise(ArgumentError)
   end
+
+  it "does not retain compare_by_identity flag when flattening elements" do
+    set = Set[1, 2, Set[3, 4]].compare_by_identity
+    set.flatten!
+    set.compare_by_identity?.should == false
+  end
+
+  it "retains compare_by_identity flag if no elements are flattened" do
+    set = Set[1, 2].compare_by_identity
+    set.flatten!
+    set.compare_by_identity?.should == true
+  end
 end
diff --git a/core/set/intersection_spec.rb b/core/set/intersection_spec.rb
index c14e1f62a..3551fe701 100644
--- a/core/set/intersection_spec.rb
+++ b/core/set/intersection_spec.rb
@@ -20,4 +20,10 @@
     -> { @set & 1 }.should.raise(ArgumentError)
     -> { @set & Object.new }.should.raise(ArgumentError)
   end
+
+  it "does not retain compare_by_identity flag" do
+    @set.compare_by_identity
+    (@set & Set[:b, :c, :d, :e]).compare_by_identity?.should == false
+    (@set & [:b, :c, :d]).compare_by_identity?.should == false
+  end
 end
diff --git a/core/set/map_spec.rb b/core/set/map_spec.rb
index fd04a8bde..6f6959fee 100644
--- a/core/set/map_spec.rb
+++ b/core/set/map_spec.rb
@@ -19,4 +19,10 @@
     @set.map! { |x| x * 2 }
     @set.should == Set[2, 4, 6, 8, 10]
   end
+
+  it "does not retain compare_by_identity flag" do
+    @set.compare_by_identity
+    @set.map! { |x| x * 2 }
+    @set.compare_by_identity?.should == false
+  end
 end
diff --git a/core/set/merge_spec.rb b/core/set/merge_spec.rb
index a2c1a7e70..c7f2cd90b 100644
--- a/core/set/merge_spec.rb
+++ b/core/set/merge_spec.rb
@@ -26,4 +26,14 @@
   it "accepts multiple arguments" do
     Set[:a, :b].merge(Set[:b, :c], [:d]).should == Set[:a, :b, :c, :d]
   end
+
+  it "retains compare_by_identity flag" do
+    set = Set[1, 2].compare_by_identity
+    set.merge([3, 4])
+    set.compare_by_identity?.should == true
+
+    set2 = Set[1, 2].compare_by_identity
+    set2.merge(Set[3, 4])
+    set2.compare_by_identity?.should == true
+  end
 end
diff --git a/core/set/minus_spec.rb b/core/set/minus_spec.rb
index 857470855..4e3387138 100644
--- a/core/set/minus_spec.rb
+++ b/core/set/minus_spec.rb
@@ -14,4 +14,10 @@
     -> { @set - 1 }.should.raise(ArgumentError)
     -> { @set - Object.new }.should.raise(ArgumentError)
   end
+
+  it "retains compare_by_identity flag" do
+    @set.compare_by_identity
+    (@set - Set[:a, :b]).compare_by_identity?.should == true
+    (@set - [:a, :b]).compare_by_identity?.should == true
+  end
 end
diff --git a/core/set/replace_spec.rb b/core/set/replace_spec.rb
index 2a51a024d..bd3a32734 100644
--- a/core/set/replace_spec.rb
+++ b/core/set/replace_spec.rb
@@ -21,4 +21,22 @@
   it "accepts any enumerable as other" do
     @set.replace([1, 2, 3]).should == Set[1, 2, 3]
   end
+
+  it "transfers compare_by_identity flag of the argument if it is a Set" do
+    set1 = Set[:a].compare_by_identity
+    set2 = Set[1, 2]
+    set1.replace(set2)
+    set1.compare_by_identity?.should == false
+
+    set3 = Set[:a]
+    set4 = Set[1, 2].compare_by_identity
+    set3.replace(set4)
+    set3.compare_by_identity?.should == true
+  end
+
+  it "retains compare_by_identity flag if the argument is a non-Set Enumerable" do
+    set1 = Set[:a].compare_by_identity
+    set1.replace([1, 2])
+    set1.compare_by_identity?.should == true
+  end
 end
diff --git a/core/set/union_spec.rb b/core/set/union_spec.rb
index 206535aae..5b15d89a3 100644
--- a/core/set/union_spec.rb
+++ b/core/set/union_spec.rb
@@ -20,4 +20,10 @@
     -> { @set | 1 }.should.raise(ArgumentError)
     -> { @set | Object.new }.should.raise(ArgumentError)
   end
+
+  it "retains compare_by_identity flag" do
+    @set.compare_by_identity
+    (@set | Set[:b, :d, :e]).compare_by_identity?.should == true
+    (@set | [:b, :d, :e]).compare_by_identity?.should == true
+  end
 end
diff --git a/language/for_spec.rb b/language/for_spec.rb
index b0f3aef40..b8a0c9deb 100644
--- a/language/for_spec.rb
+++ b/language/for_spec.rb
@@ -40,6 +40,26 @@
     end
   end
 
+  it "iterates over a list of arrays and destructures with a multi-assignment" do
+    for (i, j, k) in [[1,2,3]]
+      [i, j, k].should == [1, 2, 3]
+    end
+
+    for i, (j, k) in [[1,[2,3]]]
+      [i, j, k].should == [1, 2, 3]
+    end
+
+    # Prism-related bug
+    # https://github.com/ruby/prism/pull/4156
+    ruby_version_is "4.1" do
+      eval <<~RUBY
+      for (i, j), k in [[[1,2],3]]
+        [i, j, k].should == [1, 2, 3]
+      end
+      RUBY
+    end
+  end
+
   it "iterates over an Hash passing each key-value pair to the block" do
     k = 0
     l = 0
diff --git a/optional/capi/regexp_spec.rb b/optional/capi/regexp_spec.rb
index f233b5e3b..0a7ec4b17 100644
--- a/optional/capi/regexp_spec.rb
+++ b/optional/capi/regexp_spec.rb
@@ -17,12 +17,16 @@
     end
 
     it "returns a Regexp with the given options" do
-      @p.a_re("a", 0).options == 0
+      @p.a_re("a", 0).options.should == 0
       @p.a_re("a", Regexp::IGNORECASE).options.should == Regexp::IGNORECASE
       @p.a_re("a", Regexp::EXTENDED).options.should == Regexp::EXTENDED
       @p.a_re("a", Regexp::EXTENDED | Regexp::IGNORECASE).options.should == Regexp::EXTENDED | Regexp::IGNORECASE
       @p.a_re("a", Regexp::MULTILINE).options.should == Regexp::MULTILINE
     end
+
+    it "returns a Regexp that equals an equivalent Regexp literal" do
+      @p.a_re("^[0-9]", 0).should == /^[0-9]/
+    end
   end
 
   describe "rb_reg_nth_match" do