diff --git a/changelog/new_hidden_test_method_cop.md b/changelog/new_hidden_test_method_cop.md
new file mode 100644
index 00000000..35f83ba9
--- /dev/null
+++ b/changelog/new_hidden_test_method_cop.md
@@ -0,0 +1 @@
+* [#220](/~https://github.com/rubocop/rubocop-minitest/issues/220): Add new `Minitest/HiddenTestMethod` cop. ([@fatkodima][])
diff --git a/config/default.yml b/config/default.yml
index f49a550f..d0ad02a3 100644
--- a/config/default.yml
+++ b/config/default.yml
@@ -158,6 +158,11 @@ Minitest/GlobalExpectations:
   VersionAdded: '0.7'
   VersionChanged: '0.26'
 
+Minitest/HiddenTestMethod:
+  Description: 'Detects hidden (marked as `private` or `protected`) test methods.'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+
 Minitest/LiteralAsActualArgument:
   Description: 'This cop enforces correct order of `expected` and `actual` arguments for `assert_equal`.'
   StyleGuide: 'https://minitest.rubystyle.guide/#assert-equal-arguments-order'
diff --git a/lib/rubocop/cop/minitest/hidden_test_method.rb b/lib/rubocop/cop/minitest/hidden_test_method.rb
new file mode 100644
index 00000000..ef1eccdd
--- /dev/null
+++ b/lib/rubocop/cop/minitest/hidden_test_method.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Minitest
+      # Detects hidden (marked as `private` or `protected`) test methods. Minitest runs only
+      # test methods which are `public`.
+      #
+      # @example
+      #   # bad
+      #   class FooTest
+      #     private # or protected
+      #     def test_does_something
+      #       assert_equal 42, do_something
+      #     end
+      #   end
+      #
+      #   # good
+      #   class FooTest
+      #     def test_does_something
+      #       assert_equal 42, do_something
+      #     end
+      #   end
+      #
+      #   # good (not a test case name)
+      #   class FooTest
+      #     private # or protected
+      #     def does_something
+      #       assert_equal 42, do_something
+      #     end
+      #   end
+      #
+      #   # good (no assertions)
+      #   class FooTest
+      #     private # or protected
+      #     def test_does_something
+      #       do_something
+      #     end
+      #   end
+      #
+      class HiddenTestMethod < Base
+        include MinitestExplorationHelpers
+        include DefNode
+
+        MSG = 'Hidden test method detected. Make it public for it to run.'
+
+        def on_class(node)
+          test_cases(node).each do |test_case|
+            add_offense(test_case) if non_public?(test_case) && assertions(test_case).any?
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/rubocop/cop/minitest_cops.rb b/lib/rubocop/cop/minitest_cops.rb
index c2abc39b..a2478366 100644
--- a/lib/rubocop/cop/minitest_cops.rb
+++ b/lib/rubocop/cop/minitest_cops.rb
@@ -28,6 +28,7 @@
 require_relative 'minitest/assert_truthy'
 require_relative 'minitest/duplicate_test_run'
 require_relative 'minitest/empty_line_before_assertion_methods'
+require_relative 'minitest/hidden_test_method'
 require_relative 'minitest/test_file_name'
 require_relative 'minitest/global_expectations'
 require_relative 'minitest/literal_as_actual_argument'
diff --git a/test/rubocop/cop/minitest/hidden_test_method_test.rb b/test/rubocop/cop/minitest/hidden_test_method_test.rb
new file mode 100644
index 00000000..f863cbc8
--- /dev/null
+++ b/test/rubocop/cop/minitest/hidden_test_method_test.rb
@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class HiddenTestMethodTest < Minitest::Test
+  def test_registers_offense_when_using_private_test_method
+    assert_offense(<<~RUBY)
+      class FooTest < Minitest::Test
+        private
+        def test_does_something
+        ^^^^^^^^^^^^^^^^^^^^^^^ Hidden test method detected. Make it public for it to run.
+          assert_equal 42, do_something
+        end
+      end
+    RUBY
+  end
+
+  def test_registers_offense_when_using_protected_test_method
+    assert_offense(<<~RUBY)
+      class FooTest < Minitest::Test
+        protected
+        def test_does_something
+        ^^^^^^^^^^^^^^^^^^^^^^^ Hidden test method detected. Make it public for it to run.
+          assert_equal 42, do_something
+        end
+      end
+    RUBY
+  end
+
+  def test_registers_offense_when_using_private_test_method_outside_of_test_class
+    assert_offense(<<~RUBY)
+      class FooTest
+        private
+        def test_does_something
+        ^^^^^^^^^^^^^^^^^^^^^^^ Hidden test method detected. Make it public for it to run.
+          assert_equal 42, do_something
+        end
+      end
+    RUBY
+  end
+
+  def test_registers_offense_when_using_private_active_support_test_method
+    assert_offense(<<~RUBY)
+      class FooTest
+        private
+        test "does something"  do
+        ^^^^^^^^^^^^^^^^^^^^^^^^^ Hidden test method detected. Make it public for it to run.
+          assert_equal 42, do_something
+        end
+      end
+    RUBY
+  end
+
+  def test_does_not_register_offense_when_using_private_non_test_method_with_assertions
+    assert_no_offenses(<<~RUBY)
+      class FooTest < Minitest::Test
+        private
+        def does_something
+          assert_equal 42, do_something
+        end
+      end
+    RUBY
+  end
+
+  def test_does_not_register_offense_when_using_private_test_method_without_assertions
+    assert_no_offenses(<<~RUBY)
+      class FooTest < Minitest::Test
+        private
+        def test_does_something
+          do_something
+        end
+      end
+    RUBY
+  end
+end