1 files changed, 34 insertions, 1 deletions
diff --git a/spec/ruby/core/kernel/format_spec.rb b/spec/ruby/core/kernel/format_spec.rb
index 72fd40b952..35c752b1ab 100644
--- a/spec/ruby/core/kernel/format_spec.rb
+++ b/spec/ruby/core/kernel/format_spec.rb
@@ -1,9 +1,10 @@
 require_relative '../../spec_helper'
 require_relative 'fixtures/classes'
 
+# NOTE: most specs are in sprintf_spec.rb, this is just an alias
 describe "Kernel#format" do
   it "is a private method" do
-    Kernel.should have_private_instance_method(:format)
+    Kernel.private_instance_methods(false).should.include?(:format)
   end
 end
 
@@ -11,4 +12,36 @@ describe "Kernel.format" do
   it "is accessible as a module function" do
     Kernel.format("%s", "hello").should == "hello"
   end
+
+  describe "when $VERBOSE is true" do
+    it "warns if too many arguments are passed" do
+      code = <<~RUBY
+        $VERBOSE = true
+        format("test", 1)
+      RUBY
+
+      ruby_exe(code, args: "2>&1").should.include?("warning: too many arguments for format string")
+    end
+
+    it "does not warns if too many keyword arguments are passed" do
+      code = <<~RUBY
+        $VERBOSE = true
+        format("test %{test}", test: 1, unused: 2)
+      RUBY
+
+      ruby_exe(code, args: "2>&1").should_not.include?("warning")
+    end
+
+    ruby_bug "#20593", ""..."3.4" do
+      it "doesn't warns if keyword arguments are passed and none are used" do
+        code = <<~RUBY
+          $VERBOSE = true
+          format("test", test: 1)
+          format("test", {})
+        RUBY
+
+        ruby_exe(code, args: "2>&1").should_not.include?("warning")
+      end
+    end
+  end
 end