1 files changed, 31 insertions, 2 deletions
diff --git a/spec/ruby/core/string/index_spec.rb b/spec/ruby/core/string/index_spec.rb
index 2eeee9be87..835263a2cd 100644
--- a/spec/ruby/core/string/index_spec.rb
+++ b/spec/ruby/core/string/index_spec.rb
@@ -161,11 +161,18 @@ describe "String#index with String" do
   end
 
   it "handles a substring in a superset encoding" do
-    'abc'.force_encoding(Encoding::US_ASCII).index('é').should == nil
+    'abc'.dup.force_encoding(Encoding::US_ASCII).index('é').should == nil
   end
 
   it "handles a substring in a subset encoding" do
-    'été'.index('t'.force_encoding(Encoding::US_ASCII)).should == 1
+    'été'.index('t'.dup.force_encoding(Encoding::US_ASCII)).should == 1
+  end
+
+  it "raises an Encoding::CompatibilityError if the encodings are incompatible" do
+    str = 'abc'.dup.force_encoding("ISO-2022-JP")
+    pattern = 'b'.dup.force_encoding("EUC-JP")
+
+    -> { str.index(pattern) }.should raise_error(Encoding::CompatibilityError, "incompatible character encodings: ISO-2022-JP and EUC-JP")
   end
 end
 
@@ -224,6 +231,17 @@ describe "String#index with Regexp" do
     $~.should == nil
   end
 
+  ruby_bug "#20421", ""..."3.3" do
+    it "always clear $~" do
+      "a".index(/a/)
+      $~.should_not == nil
+
+      string = "blablabla"
+      string.index(/bla/, string.length + 1)
+      $~.should == nil
+    end
+  end
+
   it "starts the search at the given offset" do
     "blablabla".index(/.{0}/, 5).should == 5
     "blablabla".index(/.{1}/, 5).should == 5
@@ -312,6 +330,17 @@ describe "String#index with Regexp" do
     "われわわれ".index(/わ/, 3).should == 3
   end
 
+  ruby_bug "#19763", ""..."3.3.0" do
+    it "raises an Encoding::CompatibilityError if the encodings are incompatible" do
+      re = Regexp.new "れ".encode(Encoding::EUC_JP)
+      -> do
+        "あれ".index re
+      end.should raise_error(Encoding::CompatibilityError, "incompatible encoding regexp match (EUC-JP regexp with UTF-8 string)")
+    end
+  end
+
+  # The exception message was incorrectly "incompatible character encodings: UTF-8 and EUC-JP" before 3.3.0
+  # Still test that the right exception class is used before that.
   it "raises an Encoding::CompatibilityError if the encodings are incompatible" do
     re = Regexp.new "れ".encode(Encoding::EUC_JP)
     -> do