diff --git a/lib/rbs/test.rb b/lib/rbs/test.rb
index e24e1e412..a69423b45 100644
--- a/lib/rbs/test.rb
+++ b/lib/rbs/test.rb
@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "securerandom"
+require "rbs/test/guaranteed"
 require "rbs/test/observer"
 require "rbs/test/spy"
 require "rbs/test/errors"
@@ -23,6 +24,8 @@ module Test
     METHODS = Kernel.instance_method(:methods)
 
     class ArgumentsReturn
+      include Guaranteed::Inspect
+
       attr_reader :arguments
       attr_reader :exit_value
       attr_reader :exit_type
diff --git a/lib/rbs/test/guaranteed.rb b/lib/rbs/test/guaranteed.rb
new file mode 100644
index 000000000..4a1e34e6a
--- /dev/null
+++ b/lib/rbs/test/guaranteed.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+module RBS
+  module Test
+    module Guaranteed
+      module Inspect
+        EQUAL = ::BasicObject.instance_method(:equal?)
+        INSPECT = ::Kernel.instance_method(:inspect)
+        private_constant :EQUAL, :INSPECT
+
+        module_function def guaranteed_inspect(obj)
+          obj.inspect
+        rescue NoMethodError => err
+          raise unless err.name == :inspect && EQUAL.bind_call(obj, err.receiver)
+          INSPECT.bind_call(obj)
+        end
+
+        def inspect
+          string = "<#{self.class.name}:"
+
+          instance_variables.each_with_index do |variable, index|
+            string.concat ', ' unless index.zero?
+            string.concat "#{variable}: #{guaranteed_inspect(variable)}"
+          end
+
+          string.concat '>'
+        end
+      end
+    end
+  end
+end
diff --git a/lib/rbs/test/type_check.rb b/lib/rbs/test/type_check.rb
index e369f5f82..ac0edbc35 100644
--- a/lib/rbs/test/type_check.rb
+++ b/lib/rbs/test/type_check.rb
@@ -136,7 +136,7 @@ def zip_keyword_args(hash, fun)
       end
 
       def keyword?(value)
-        value.is_a?(Hash) && value.keys.all? {|key| key.is_a?(Symbol) }
+        Hash === value && value.each_key.all?(Symbol)
       end
 
       def zip_args(args, fun, &block)
@@ -310,7 +310,7 @@ def value(val, type)
         when Types::Variable
           true
         when Types::Literal
-          val == type.literal
+          type.literal == val
         when Types::Union
           type.types.any? {|type| value(val, type) }
         when Types::Intersection
diff --git a/test/stdlib/Pathname_test.rb b/test/stdlib/Pathname_test.rb
index f11449fd8..e2433508a 100644
--- a/test/stdlib/Pathname_test.rb
+++ b/test/stdlib/Pathname_test.rb
@@ -606,8 +606,9 @@ def test_relative_path_from
                      Pathname('.'), :relative_path_from, Pathname('.')
     assert_send_type '(String) -> Pathname',
                      Pathname('.'), :relative_path_from, '.'
-    assert_send_type '(ToStr) -> Pathname',
-                     Pathname('.'), :relative_path_from, ToStr.new('.')
+
+    assert_send_type '(_ToStr) -> Pathname',
+                     Pathname('.'), :relative_path_from, ToStr.new('.').__with_object_methods(:is_a?)
   end
 
   def test_rename
diff --git a/test/stdlib/ThreadQueue_test.rb b/test/stdlib/ThreadQueue_test.rb
index 389c4569e..c8769bc83 100644
--- a/test/stdlib/ThreadQueue_test.rb
+++ b/test/stdlib/ThreadQueue_test.rb
@@ -63,7 +63,7 @@ def test_pop
     q.pop(true)
     q.pop(false)
     q.pop(timeout: 0.2)
-    q.pop(timeout: ToF.new(0.1))
+    q.pop(timeout: ToF.new(0.1).__with_object_methods(:==))
   end
 
   def test_push
diff --git a/test/stdlib/ThreadSizedQueue_test.rb b/test/stdlib/ThreadSizedQueue_test.rb
index 7a83cd8c7..a42633f4d 100644
--- a/test/stdlib/ThreadSizedQueue_test.rb
+++ b/test/stdlib/ThreadSizedQueue_test.rb
@@ -37,6 +37,6 @@ def test_push
     q.push(:a, true)
     q.push(:a, false)
     q.push(:a, timeout: 0.1)
-    q.push(:a, timeout: ToF.new(0.1))
+    q.push(:a, timeout: ToF.new(0.1).__with_object_methods(:==))
   end
 end
diff --git a/test/stdlib/Warning_test.rb b/test/stdlib/Warning_test.rb
index e7d89ebd4..e8b612bc2 100644
--- a/test/stdlib/Warning_test.rb
+++ b/test/stdlib/Warning_test.rb
@@ -16,7 +16,7 @@ def test_aref
     refute_send_type "(Symbol) -> bool",
         Warning, :[], :unknown_category
 
-    refute_send_type "(ToSym) -> bool",
+    refute_send_type "(_ToSym) -> bool",
         Warning, :[], ToSym.new(WARNING_CATEGORIES.first)
   end
 
@@ -29,7 +29,7 @@ def test_aset
     refute_send_type "(Symbol, Rational) -> Rational",
         Warning, :[]=, :unknown_category, 1r
 
-    refute_send_type "(ToSym, Rational) -> Rational",
+    refute_send_type "(_ToSym, Rational) -> Rational",
         Warning, :[]=, ToSym.new(WARNING_CATEGORIES.first), 1r
   end
 end
@@ -66,7 +66,7 @@ def test_warn
     assert_send_type "(::String, category: nil) -> nil",
         Warning, :warn, 'message', category: nil
 
-    refute_send_type "(::String, category: ToSym) -> nil",
+    refute_send_type "(::String, category: _ToSym) -> nil",
         Warning, :warn, 'message', category: ToSym.new(WARNING_CATEGORIES.first)
 
     refute_send_type "(::String, category: ::Symbol) -> nil",
diff --git a/test/stdlib/json/JSON_test.rb b/test/stdlib/json/JSON_test.rb
index b4a3a00d5..66504f8d4 100644
--- a/test/stdlib/json/JSON_test.rb
+++ b/test/stdlib/json/JSON_test.rb
@@ -1,6 +1,26 @@
 require_relative "../test_helper"
 require "json"
 
+class JsonToStr
+  def initialize(value = "")
+    @value = value
+  end
+
+  def to_str
+    @value
+  end
+end
+
+class JsonToS
+  def initialize(value = "")
+    @value = value
+  end
+
+  def to_s
+    @value
+  end
+end
+
 class JSONSingletonTest < Test::Unit::TestCase
   include TypeAssertions
 
@@ -9,26 +29,26 @@ class JSONSingletonTest < Test::Unit::TestCase
 
   def test_aref
     assert_send_type "(String) -> 42", JSON, :[], "42"
-    assert_send_type "(ToStr) -> 42", JSON, :[], ToStr.new("42")
+    assert_send_type "(_ToStr) -> 42", JSON, :[], JsonToStr.new("42")
     assert_send_type "(ToJson) -> String", JSON, :[], ToJson.new
     assert_send_type "(ToJson, indent: String) -> String", JSON, :[], ToJson.new, { indent: "\t" }
   end
 
   def test_create_id
-    JSON.create_id = ToS.new("json_class")
-    assert_send_type "() -> ToS", JSON, :create_id
+    JSON.create_id = JsonToS.new("json_class")
+    assert_send_type "() -> _ToS", JSON, :create_id
     JSON.create_id = "json_class"
     assert_send_type "() -> String", JSON, :create_id
   end
 
   def test_create_id_eq
-    assert_send_type "(ToS) -> ToS", JSON, :create_id=, ToS.new("json_class")
+    assert_send_type "(_ToS) -> _ToS", JSON, :create_id=, JsonToS.new("json_class")
     assert_send_type "(String) -> String", JSON, :create_id=, "json_class"
   end
 
   def test_deep_const_get
     assert_send_type "(String) -> String", JSON, :deep_const_get, "File::SEPARATOR"
-    assert_send_type "(ToS) -> String", JSON, :deep_const_get, ToS.new("File::SEPARATOR")
+    assert_send_type "(_ToS) -> String", JSON, :deep_const_get, JsonToS.new("File::SEPARATOR")
   end
 
   def test_dump
@@ -76,12 +96,12 @@ def test_generator=
   def test_iconv
     assert_send_type "(Encoding, Encoding, String) -> String", JSON, :iconv, Encoding::UTF_8, Encoding::UTF_16, "".encode(Encoding::UTF_16)
     assert_send_type "(String, String, String) -> String", JSON, :iconv, 'UTF-8', 'UTF-16', "".encode(Encoding::UTF_16)
-    assert_send_type "(ToStr, ToStr, String) -> String", JSON, :iconv, ToStr.new('UTF-8'), ToStr.new('UTF-16'), "".encode(Encoding::UTF_16)
+    assert_send_type "(_ToStr, _ToStr, String) -> String", JSON, :iconv, JsonToStr.new('UTF-8'), JsonToStr.new('UTF-16'), "".encode(Encoding::UTF_16)
   end
 
   def test_load
     assert_send_type "(String) -> 42", JSON, :load, "42"
-    assert_send_type "(ToStr) -> 42", JSON, :load, ToStr.new("42")
+    assert_send_type "(_ToStr) -> 42", JSON, :load, JsonToStr.new("42")
     assert_send_type "(JsonToReadableIO) -> 42", JSON, :load, JsonToReadableIO.new
     assert_send_type "(JsonRead) -> 42", JSON, :load, JsonRead.new
     assert_send_type "(String, Proc) -> 42", JSON, :load, "42", proc { }
@@ -98,13 +118,13 @@ def test_load_default_options_eq
 
   def test_parse
     assert_send_type "(String) -> 42", JSON, :parse, "42"
-    assert_send_type "(ToStr) -> 42", JSON, :parse, ToStr.new("42")
+    assert_send_type "(_ToStr) -> 42", JSON, :parse, JsonToStr.new("42")
     assert_send_type "(String, Hash[untyped, untyped]) -> 42", JSON, :parse, "42", { allow_nan: true }
   end
 
   def test_parse!
     assert_send_type "(String) -> 42", JSON, :parse!, "42"
-    assert_send_type "(ToStr) -> 42", JSON, :parse!, ToStr.new("42")
+    assert_send_type "(_ToStr) -> 42", JSON, :parse!, JsonToStr.new("42")
     assert_send_type "(String, Hash[untyped, untyped]) -> 42", JSON, :parse!, "42", { allow_nan: true }
   end
 
@@ -132,7 +152,7 @@ def test_recurse_proc
 
   def test_restore
     assert_send_type "(String) -> 42", JSON, :restore, "42"
-    assert_send_type "(ToStr) -> 42", JSON, :restore, ToStr.new("42")
+    assert_send_type "(_ToStr) -> 42", JSON, :restore, JsonToStr.new("42")
     assert_send_type "(JsonToReadableIO) -> 42", JSON, :restore, JsonToReadableIO.new
     assert_send_type "(JsonRead) -> 42", JSON, :restore, JsonRead.new
     assert_send_type "(String, Proc) -> 42", JSON, :restore, "42", proc { }
@@ -192,7 +212,7 @@ def test_generate
 
   def test_load
     assert_send_type "(String) -> 42", MyJSON.new, :load, "42"
-    assert_send_type "(ToStr) -> 42", MyJSON.new, :load, ToStr.new("42")
+    assert_send_type "(_ToStr) -> 42", MyJSON.new, :load, JsonToStr.new("42")
     assert_send_type "(JsonToReadableIO) -> 42", MyJSON.new, :load, JsonToReadableIO.new
     assert_send_type "(JsonRead) -> 42", MyJSON.new, :load, JsonRead.new
     assert_send_type "(String, Proc) -> 42", MyJSON.new, :load, "42", proc { }
@@ -201,13 +221,13 @@ def test_load
 
   def test_parse
     assert_send_type "(String) -> 42", MyJSON.new, :parse, "42"
-    assert_send_type "(ToStr) -> 42", MyJSON.new, :parse, ToStr.new("42")
+    assert_send_type "(_ToStr) -> 42", MyJSON.new, :parse, JsonToStr.new("42")
     assert_send_type "(String, Hash[untyped, untyped]) -> 42", MyJSON.new, :parse, "42", { allow_nan: true }
   end
 
   def test_parse!
     assert_send_type "(String) -> 42", MyJSON.new, :parse!, "42"
-    assert_send_type "(ToStr) -> 42", MyJSON.new, :parse!, ToStr.new("42")
+    assert_send_type "(_ToStr) -> 42", MyJSON.new, :parse!, JsonToStr.new("42")
     assert_send_type "(String, Hash[untyped, untyped]) -> 42", MyJSON.new, :parse!, "42", { allow_nan: true }
   end
 
@@ -227,7 +247,7 @@ def test_recurse_proc
 
   def test_restore
     assert_send_type "(String) -> 42", MyJSON.new, :restore, "42"
-    assert_send_type "(ToStr) -> 42", MyJSON.new, :restore, ToStr.new("42")
+    assert_send_type "(_ToStr) -> 42", MyJSON.new, :restore, JsonToStr.new("42")
     assert_send_type "(JsonToReadableIO) -> 42", MyJSON.new, :restore, JsonToReadableIO.new
     assert_send_type "(JsonRead) -> 42", MyJSON.new, :restore, JsonRead.new
     assert_send_type "(String, Proc) -> 42", MyJSON.new, :restore, "42", proc { }
diff --git a/test/stdlib/rubygems/GemVersion_test.rb b/test/stdlib/rubygems/GemVersion_test.rb
index 5f8b9abb1..1db502253 100644
--- a/test/stdlib/rubygems/GemVersion_test.rb
+++ b/test/stdlib/rubygems/GemVersion_test.rb
@@ -8,15 +8,15 @@ class GemVersionSingletonTest < Test::Unit::TestCase
   def test_correct?
     assert_send_type  "(String) -> bool",
                       Gem::Version, :correct?, "1.2.3"
-    assert_send_type  "(ToS) -> bool",
-                      Gem::Version, :correct?, ToS.new
+    assert_send_type  "(_ToS) -> bool",
+                      Gem::Version, :correct?, ToS.new.__with_object_methods(:respond_to?, :nil?)
   end
 
   def test_create
     assert_send_type  "(String) -> Gem::Version",
                       Gem::Version, :create, "1.2.3"
-    assert_send_type  "(ToS) -> Gem::Version",
-                      Gem::Version, :create, ToS.new("1.2.3")
+    assert_send_type  "(_ToS) -> Gem::Version",
+                      Gem::Version, :create, ToS.new("1.2.3").__with_object_methods(:respond_to?, :hash, :nil?, :is_a?)
     assert_send_type  "(Gem::Version) -> Gem::Version",
                       Gem::Version, :create, Gem::Version.new("1.2.3")
   end
@@ -24,8 +24,8 @@ def test_create
   def test_new
     assert_send_type  "(String) -> Gem::Version",
                       Gem::Version, :new, "1.2.3"
-    assert_send_type  "(ToS) -> Gem::Version",
-                      Gem::Version, :new, ToS.new("1.2.3")
+    assert_send_type  "(_ToS) -> Gem::Version",
+                      Gem::Version, :new, ToS.new("1.2.3").__with_object_methods(:respond_to?, :hash, :nil?, :is_a?)
   end
 end
 
diff --git a/test/stdlib/test_helper.rb b/test/stdlib/test_helper.rb
index 2224d8ae5..0851d5fbe 100644
--- a/test/stdlib/test_helper.rb
+++ b/test/stdlib/test_helper.rb
@@ -525,7 +525,24 @@ def assert_type(type, value)
   end
 end
 
-class ToIO
+class BlankSlate < BasicObject
+  instance_methods.each do |im|
+    next if %i[__send__ __id__].include? im
+    undef_method im
+  end
+
+  def __with_object_methods(*methods)
+    methods.each do |method|
+      singleton_class = ::Object.instance_method(:singleton_class).bind_call(self)
+      singleton_class.instance_eval do
+        define_method method, ::Object.instance_method(method)
+      end
+    end
+    self
+  end
+end
+
+class ToIO < BlankSlate
   def initialize(io = $stdout)
     @io = io
   end
@@ -535,7 +552,7 @@ def to_io
   end
 end
 
-class ToI
+class ToI < BlankSlate
   def initialize(value = 3)
     @value = value
   end
@@ -545,7 +562,7 @@ def to_i
   end
 end
 
-class ToInt
+class ToInt < BlankSlate
   def initialize(value = 3)
     @value = value
   end
@@ -555,7 +572,7 @@ def to_int
   end
 end
 
-class ToF
+class ToF < BlankSlate
   def initialize(value = 0.1)
     @value = value
   end
@@ -565,7 +582,7 @@ def to_f
   end
 end
 
-class ToStr
+class ToStr < BlankSlate
   def initialize(value = "")
     @value = value
   end
@@ -575,7 +592,7 @@ def to_str
   end
 end
 
-class ToS
+class ToS < BlankSlate
   def initialize(value = "")
     @value = value
   end
@@ -585,8 +602,7 @@ def to_s
   end
 end
 
-
-class ToSym
+class ToSym < BlankSlate
   def initialize(value = :&)
     @value = value
   end
@@ -596,7 +612,7 @@ def to_sym
   end
 end
 
-class ToA
+class ToA < BlankSlate
   def initialize(*args)
     @args = args
   end
@@ -606,7 +622,7 @@ def to_a
   end
 end
 
-class ToArray
+class ToArray < BlankSlate
   def initialize(*args)
     @args = args
   end
@@ -616,7 +632,7 @@ def to_ary
   end
 end
 
-class ToHash
+class ToHash < BlankSlate
   def initialize(hash = { 'hello' => 'world' })
     @hash = hash
   end
@@ -626,7 +642,7 @@ def to_hash
   end
 end
 
-class ToPath
+class ToPath < BlankSlate
   def initialize(value = "")
     @value = value
   end
@@ -636,7 +652,7 @@ def to_path
   end
 end
 
-class Each
+class Each < BlankSlate
   def initialize(*args)
     @args = args
   end
@@ -661,7 +677,7 @@ def write(*vals)
 class ToJson
 end
 
-class Rand
+class Rand < BlankSlate
   def rand(max)
     max - 1
   end
@@ -690,19 +706,19 @@ def to_io
   end
 end
 
-class Enum
+class Enum < BlankSlate
   def initialize(*args)
     @args = args
   end
 
-  include Enumerable
+  include ::Enumerable
 
   def each(&block)
     @args.each(&block)
   end
 end
 
-class ArefFromStringToString
+class ArefFromStringToString < BlankSlate
   def [](str)
     "!"
   end