5 files changed, 71 insertions, 11 deletions
diff --git a/test/-ext-/string/test_capacity.rb b/test/-ext-/string/test_capacity.rb
index 0cb7c00761..df000f7cdb 100644
--- a/test/-ext-/string/test_capacity.rb
+++ b/test/-ext-/string/test_capacity.rb
@@ -23,7 +23,7 @@ class Test_StringCapacity < Test::Unit::TestCase
   def test_s_new_capacity
     assert_equal("", String.new(capacity: 1000))
     assert_equal(String, String.new(capacity: 1000).class)
-    assert_equal(10000, capa(String.new(capacity: 10000)))
+    assert_equal(10_000, capa(String.new(capacity: 10_000)))
 
     assert_equal("", String.new(capacity: -1000))
     assert_equal(capa(String.new(capacity: -10000)), capa(String.new(capacity: -1000)))
@@ -66,11 +66,7 @@ class Test_StringCapacity < Test::Unit::TestCase
   end
 
   def embed_header_size
-    if GC.using_rvargc?
-      2 * RbConfig::SIZEOF['void*'] + RbConfig::SIZEOF['long']
-    else
-      2 * RbConfig::SIZEOF['void*']
-    end
+    GC::INTERNAL_CONSTANTS[:RBASIC_SIZE] + RbConfig::SIZEOF['void*']
   end
 
   def max_embed_len
diff --git a/test/-ext-/string/test_fstring.rb b/test/-ext-/string/test_fstring.rb
index 5a3456c566..fcec6be543 100644
--- a/test/-ext-/string/test_fstring.rb
+++ b/test/-ext-/string/test_fstring.rb
@@ -15,19 +15,27 @@ class Test_String_Fstring < Test::Unit::TestCase
   def test_rb_enc_interned_str_autoloaded_encoding
     assert_separately([], <<~RUBY)
       require '-test-/string'
-      assert_include(Encoding::Windows_31J.inspect, 'autoload')
-      Bug::String.rb_enc_interned_str(Encoding::Windows_31J)
+      assert_include(Encoding::CESU_8.inspect, 'autoload')
+      Bug::String.rb_enc_interned_str(Encoding::CESU_8)
     RUBY
   end
 
+  def test_rb_enc_interned_str_null_encoding
+    assert_equal Encoding::ASCII_8BIT, Bug::String.rb_enc_interned_str(nil).encoding
+  end
+
   def test_rb_enc_str_new_autoloaded_encoding
     assert_separately([], <<~RUBY)
       require '-test-/string'
-      assert_include(Encoding::Windows_31J.inspect, 'autoload')
-      Bug::String.rb_enc_str_new(Encoding::Windows_31J)
+      assert_include(Encoding::CESU_8.inspect, 'autoload')
+      Bug::String.rb_enc_str_new(Encoding::CESU_8)
     RUBY
   end
 
+  def test_rb_enc_str_new_null_encoding
+    assert_equal Encoding::ASCII_8BIT, Bug::String.rb_enc_str_new(nil).encoding
+  end
+
   def test_instance_variable
     str = __method__.to_s * 3
     str.instance_variable_set(:@test, 42)
@@ -49,6 +57,10 @@ class Test_String_Fstring < Test::Unit::TestCase
     assert_raise(TypeError) {fstr.singleton_class}
   end
 
+  def test_fake_str
+    assert_equal([*"a".."z"].join(""), Bug::String.fstring_fake_str)
+  end
+
   class S < String
   end
 
diff --git a/test/-ext-/string/test_interned_str.rb b/test/-ext-/string/test_interned_str.rb
index 340dba41e8..a81cb59aa5 100644
--- a/test/-ext-/string/test_interned_str.rb
+++ b/test/-ext-/string/test_interned_str.rb
@@ -9,4 +9,9 @@ class Test_RbInternedStr < Test::Unit::TestCase
     src << "b" * 20
     assert_equal "a" * 20, interned_str
   end
+
+  def test_interned_str_encoding
+    src = :ascii.name
+    assert_equal Encoding::US_ASCII, Bug::String.rb_interned_str_dup(src).encoding
+  end
 end
diff --git a/test/-ext-/string/test_set_len.rb b/test/-ext-/string/test_set_len.rb
index 67ba961194..1531d76167 100644
--- a/test/-ext-/string/test_set_len.rb
+++ b/test/-ext-/string/test_set_len.rb
@@ -34,4 +34,51 @@ class Test_StrSetLen < Test::Unit::TestCase
     assert_equal 128, Bug::String.capacity(str)
     assert_equal 127, str.set_len(127).bytesize, bug12757
   end
+
+  def test_coderange_after_append
+    u = -"\u3042"
+    str = Bug::String.new(encoding: Encoding::UTF_8)
+    bsize = u.bytesize
+    str.append(u)
+    assert_equal 0, str.bytesize
+    str.set_len(bsize)
+    assert_equal bsize, str.bytesize
+    assert_predicate str, :valid_encoding?
+    assert_not_predicate str, :ascii_only?
+    assert_equal u, str
+  end
+
+  def test_coderange_after_trunc
+    u = -"\u3042"
+    bsize = u.bytesize
+    str = Bug::String.new(u)
+    str.set_len(bsize - 1)
+    assert_equal bsize - 1, str.bytesize
+    assert_not_predicate str, :valid_encoding?
+    assert_not_predicate str, :ascii_only?
+    str.append(u.byteslice(-1))
+    str.set_len(bsize)
+    assert_equal bsize, str.bytesize
+    assert_predicate str, :valid_encoding?
+    assert_not_predicate str, :ascii_only?
+    assert_equal u, str
+  end
+
+  def test_valid_encoding_after_resized
+    s = "\0\0".force_encoding(Encoding::UTF_16BE)
+    str = Bug::String.new(s)
+    assert_predicate str, :valid_encoding?
+    str.resize(1)
+    assert_not_predicate str, :valid_encoding?
+    str.resize(2)
+    assert_predicate str, :valid_encoding?
+    str.resize(3)
+    assert_not_predicate str, :valid_encoding?
+
+    s = "\xDB\x00\xDC\x00".force_encoding(Encoding::UTF_16BE)
+    str = Bug::String.new(s)
+    assert_predicate str, :valid_encoding?
+    str.resize(2)
+    assert_not_predicate str, :valid_encoding?
+  end
 end
diff --git a/test/-ext-/string/test_too_many_dummy_encodings.rb b/test/-ext-/string/test_too_many_dummy_encodings.rb
index 4d71fd1d72..b96b40db7b 100644
--- a/test/-ext-/string/test_too_many_dummy_encodings.rb
+++ b/test/-ext-/string/test_too_many_dummy_encodings.rb
@@ -4,7 +4,7 @@ require "-test-/string"
 
 class Test_TooManyDummyEncodings < Test::Unit::TestCase
   def test_exceed_encoding_table_size
-    assert_separately(%w[--disable=gems], "#{<<~"begin;"}\n#{<<~'end;'}")
+    assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
     begin;
       require "-test-/string"
       assert_raise_with_message(EncodingError, /too many encoding/) do