diff --git a/test/stdlib/json/JSONBigDecimal_test.rb b/test/stdlib/json/JSONBigDecimal_test.rb
index e63c9b4599..9187ae6639 100644
--- a/test/stdlib/json/JSONBigDecimal_test.rb
+++ b/test/stdlib/json/JSONBigDecimal_test.rb
@@ -1,5 +1,6 @@
 require_relative "../test_helper"
 require "json"
+return if Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
 require "json/add/bigdecimal"
 
 class JSONBigDecimalSingletonTest < Test::Unit::TestCase
diff --git a/test/stdlib/json/JSONComplex_test.rb b/test/stdlib/json/JSONComplex_test.rb
index b9fc36772b..055c2c371b 100644
--- a/test/stdlib/json/JSONComplex_test.rb
+++ b/test/stdlib/json/JSONComplex_test.rb
@@ -1,5 +1,6 @@
 require_relative "../test_helper"
 require "json"
+return if Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
 require "json/add/complex"
 
 class JSONComplexSingletonTest < Test::Unit::TestCase
diff --git a/test/stdlib/json/JSONDateTime_test.rb b/test/stdlib/json/JSONDateTime_test.rb
index fd3c50d632..3aedb9d15c 100644
--- a/test/stdlib/json/JSONDateTime_test.rb
+++ b/test/stdlib/json/JSONDateTime_test.rb
@@ -1,5 +1,6 @@
 require_relative "../test_helper"
 require "json"
+return if Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
 require "json/add/date_time"
 
 class JSONDateTimeSingletonTest < Test::Unit::TestCase
diff --git a/test/stdlib/json/JSONDate_test.rb b/test/stdlib/json/JSONDate_test.rb
index a2d317fa19..c331762fb0 100644
--- a/test/stdlib/json/JSONDate_test.rb
+++ b/test/stdlib/json/JSONDate_test.rb
@@ -1,5 +1,6 @@
 require_relative "../test_helper"
 require "json"
+return if Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
 require "json/add/date"
 
 class JSONDateSingletonTest < Test::Unit::TestCase
diff --git a/test/stdlib/json/JSONException_test.rb b/test/stdlib/json/JSONException_test.rb
index 42cf2c408b..060de5b9f2 100644
--- a/test/stdlib/json/JSONException_test.rb
+++ b/test/stdlib/json/JSONException_test.rb
@@ -1,5 +1,6 @@
 require_relative "../test_helper"
 require "json"
+return if Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
 require "json/add/exception"
 
 class JSONExceptionSingletonTest < Test::Unit::TestCase
diff --git a/test/stdlib/json/JSONOpenStruct_test.rb b/test/stdlib/json/JSONOpenStruct_test.rb
index 4aacb54810..28ed9b54d4 100644
--- a/test/stdlib/json/JSONOpenStruct_test.rb
+++ b/test/stdlib/json/JSONOpenStruct_test.rb
@@ -1,5 +1,6 @@
 require_relative "../test_helper"
 require "json"
+return if Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
 require "json/add/ostruct"
 
 class JSONOpenStructSingletonTest < Test::Unit::TestCase
diff --git a/test/stdlib/json/JSONRange_test.rb b/test/stdlib/json/JSONRange_test.rb
index e5a7ba2a1c..807b5158f6 100644
--- a/test/stdlib/json/JSONRange_test.rb
+++ b/test/stdlib/json/JSONRange_test.rb
@@ -1,5 +1,6 @@
 require_relative "../test_helper"
 require "json"
+return if Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
 require "json/add/range"
 
 class JSONRangeSingletonTest < Test::Unit::TestCase
diff --git a/test/stdlib/json/JSONRational_test.rb b/test/stdlib/json/JSONRational_test.rb
index 61c9fa697d..0d81ccc7b7 100644
--- a/test/stdlib/json/JSONRational_test.rb
+++ b/test/stdlib/json/JSONRational_test.rb
@@ -1,5 +1,6 @@
 require_relative "../test_helper"
 require "json"
+return if Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
 require "json/add/rational"
 
 class JSONRationalSingletonTest < Test::Unit::TestCase
diff --git a/test/stdlib/json/JSONRegexp_test.rb b/test/stdlib/json/JSONRegexp_test.rb
index b30b794153..c2bb62f853 100644
--- a/test/stdlib/json/JSONRegexp_test.rb
+++ b/test/stdlib/json/JSONRegexp_test.rb
@@ -1,5 +1,6 @@
 require_relative "../test_helper"
 require "json"
+return if Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
 require "json/add/regexp"
 
 class JSONRegexpSingletonTest < Test::Unit::TestCase
diff --git a/test/stdlib/json/JSONSet_test.rb b/test/stdlib/json/JSONSet_test.rb
index 339c83950c..d75a057ced 100644
--- a/test/stdlib/json/JSONSet_test.rb
+++ b/test/stdlib/json/JSONSet_test.rb
@@ -1,5 +1,6 @@
 require_relative "../test_helper"
 require "json"
+return if Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
 require "json/add/set"
 
 class JSONSetSingletonTest < Test::Unit::TestCase
diff --git a/test/stdlib/json/JSONStruct_test.rb b/test/stdlib/json/JSONStruct_test.rb
index 422c9a8152..3c606eeb90 100644
--- a/test/stdlib/json/JSONStruct_test.rb
+++ b/test/stdlib/json/JSONStruct_test.rb
@@ -1,5 +1,6 @@
 require_relative "../test_helper"
 require "json"
+return if Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
 require "json/add/struct"
 
 class JSONStructSingletonTest < Test::Unit::TestCase
diff --git a/test/stdlib/json/JSONSymbol_test.rb b/test/stdlib/json/JSONSymbol_test.rb
index e1dc006c0e..080bc3afd0 100644
--- a/test/stdlib/json/JSONSymbol_test.rb
+++ b/test/stdlib/json/JSONSymbol_test.rb
@@ -1,5 +1,6 @@
 require_relative "../test_helper"
 require "json"
+return if Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
 require "json/add/symbol"
 
 class JSONSymbolSingletonTest < Test::Unit::TestCase
diff --git a/test/stdlib/json/JSONTime_test.rb b/test/stdlib/json/JSONTime_test.rb
index 53fc174b17..f62eca79eb 100644
--- a/test/stdlib/json/JSONTime_test.rb
+++ b/test/stdlib/json/JSONTime_test.rb
@@ -1,5 +1,6 @@
 require_relative "../test_helper"
 require "json"
+return if Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
 require "json/add/time"
 
 class JSONTimeSingletonTest < Test::Unit::TestCase
diff --git a/test/stdlib/json/JSON_test.rb b/test/stdlib/json/JSON_test.rb
index 8b63cfe389..80004feaac 100644
--- a/test/stdlib/json/JSON_test.rb
+++ b/test/stdlib/json/JSON_test.rb
@@ -2,6 +2,12 @@
 require "json"
 require "tempfile"
 
+module JSONVersionTestHelper
+  def json_version_3_or_later?
+    Gem::Version.new(JSON::VERSION).release >= Gem::Version.new("3.0.0")
+  end
+end
+
 class JsonToStr
   def initialize(value = "")
     @value = value
@@ -24,6 +30,7 @@ def to_s
 
 class JSONSingletonTest < Test::Unit::TestCase
   include TestHelper
+  include JSONVersionTestHelper
 
   library "json"
   testing "singleton(::JSON)"
@@ -36,6 +43,8 @@ def test_aref
   end
 
   def test_create_id
+    omit_if json_version_3_or_later?
+
     JSON.create_id = JsonToS.new("json_class")
     assert_send_type "() -> _ToS", JSON, :create_id
     JSON.create_id = "json_class"
@@ -43,16 +52,21 @@ def test_create_id
   end
 
   def test_create_id_eq
+    omit_if json_version_3_or_later?
+
     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_dump
     assert_send_type "(ToJson) -> String", JSON, :dump, ToJson.new
-    assert_send_type "(ToJson, Integer) -> String", JSON, :dump, ToJson.new, 100
     assert_send_type "(ToJson, JsonToWritableIO) -> JsonWrite", JSON, :dump, ToJson.new, JsonToWritableIO.new
     assert_send_type "(ToJson, JsonWrite) -> JsonWrite", JSON, :dump, ToJson.new, JsonWrite.new
-    assert_send_type "(ToJson, JsonWrite, Integer) -> JsonWrite", JSON, :dump, ToJson.new, JsonWrite.new, 100
+
+    unless json_version_3_or_later?
+      assert_send_type "(ToJson, Integer) -> String", JSON, :dump, ToJson.new, 100
+      assert_send_type "(ToJson, JsonWrite, Integer) -> JsonWrite", JSON, :dump, ToJson.new, JsonWrite.new, 100
+    end
   end
 
   def test_generate
@@ -74,7 +88,10 @@ def test_load
     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 { |a| a }
-    assert_send_type "(String, Proc, Hash[untyped, untyped]) -> 42", JSON, :load, "42", proc { |a| a }, { alllow_nan: true }
+
+    unless json_version_3_or_later?
+      assert_send_type "(String, Proc, Hash[untyped, untyped]) -> 42", JSON, :load, "42", proc { |a| a }, { alllow_nan: true }
+    end
   end
 
   def test_load_file
@@ -83,7 +100,9 @@ def test_load_file
       f.close
 
       assert_send_type "(String) -> untyped", JSON, :load_file, f.path
-      assert_send_type "(String, Hash[untyped, untyped]) -> untyped", JSON, :load_file, f.path, { allow_nan: true }
+      unless json_version_3_or_later?
+        assert_send_type "(String, Hash[untyped, untyped]) -> untyped", JSON, :load_file, f.path, { allow_nan: true }
+      end
     end
   end
 
@@ -93,20 +112,26 @@ def test_load_file!
       f.close
 
       assert_send_type "(String) -> untyped", JSON, :load_file!, f.path
-      assert_send_type "(String, Hash[untyped, untyped]) -> untyped", JSON, :load_file!, f.path, { allow_nan: true }
+      unless json_version_3_or_later?
+        assert_send_type "(String, Hash[untyped, untyped]) -> untyped", JSON, :load_file!, f.path, { allow_nan: true }
+      end
     end
   end
 
   def test_parse
     assert_send_type "(String) -> 42", JSON, :parse, "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 }
+    unless json_version_3_or_later?
+      assert_send_type "(String, Hash[untyped, untyped]) -> 42", JSON, :parse, "42", { allow_nan: true }
+    end
   end
 
   def test_parse!
     assert_send_type "(String) -> 42", JSON, :parse!, "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 }
+    unless json_version_3_or_later?
+      assert_send_type "(String, Hash[untyped, untyped]) -> 42", JSON, :parse!, "42", { allow_nan: true }
+    end
   end
 
   def test_parser
@@ -133,6 +158,7 @@ def test_state_eq
 
 class JSONInstanceTest < Test::Unit::TestCase
   include TestHelper
+  include JSONVersionTestHelper
 
   class MyJSON
     include JSON
@@ -147,10 +173,13 @@ def load_default_options
 
   def test_dump
     assert_send_type "(ToJson) -> String", MyJSON.new, :dump, ToJson.new
-    assert_send_type "(ToJson, Integer) -> String", MyJSON.new, :dump, ToJson.new, 100
     assert_send_type "(ToJson, JsonToWritableIO) -> JsonWrite", MyJSON.new, :dump, ToJson.new, JsonToWritableIO.new
     assert_send_type "(ToJson, JsonWrite) -> JsonWrite", MyJSON.new, :dump, ToJson.new, JsonWrite.new
-    assert_send_type "(ToJson, JsonWrite, Integer) -> JsonWrite", MyJSON.new, :dump, ToJson.new, JsonWrite.new, 100
+
+    unless json_version_3_or_later?
+      assert_send_type "(ToJson, Integer) -> String", MyJSON.new, :dump, ToJson.new, 100
+      assert_send_type "(ToJson, JsonWrite, Integer) -> JsonWrite", MyJSON.new, :dump, ToJson.new, JsonWrite.new, 100
+    end
   end
 
   def test_generate
@@ -161,13 +190,17 @@ def test_generate
   def test_parse
     assert_send_type "(String) -> 42", MyJSON.new, :parse, "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 }
+    unless json_version_3_or_later?
+      assert_send_type "(String, Hash[untyped, untyped]) -> 42", MyJSON.new, :parse, "42", { allow_nan: true }
+    end
   end
 
   def test_parse!
     assert_send_type "(String) -> 42", MyJSON.new, :parse!, "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 }
+    unless json_version_3_or_later?
+      assert_send_type "(String, Hash[untyped, untyped]) -> 42", MyJSON.new, :parse!, "42", { allow_nan: true }
+    end
   end
 
   def test_pretty_generate