1 files changed, 30 insertions, 3 deletions
diff --git a/spec/ruby/core/string/unpack1_spec.rb b/spec/ruby/core/string/unpack1_spec.rb
index 3b3b879f75..ee10042eb8 100644
--- a/spec/ruby/core/string/unpack1_spec.rb
+++ b/spec/ruby/core/string/unpack1_spec.rb
@@ -20,8 +20,22 @@ describe "String#unpack1" do
     "؈".unpack1("C", offset: 1).should == 136
   end
 
-  it "raises an ArgumentError when the offset is negative" do
-    -> { "a".unpack1("C", offset: -1) }.should raise_error(ArgumentError, "offset can't be negative")
+  describe "when the offset is negative" do
+    ruby_version_is "4.1" do
+      it "starts unpacking from the end" do
+        "abc".unpack1("C", offset: -2).should == 98
+      end
+
+      it "raises an ArgumentError if it is less than -length" do
+        -> { "a".unpack1("C", offset: -2) }.should.raise(ArgumentError, "offset outside of string")
+      end
+    end
+
+    ruby_version_is ""..."4.1" do
+      it "raises an ArgumentError" do
+        -> { "a".unpack1("C", offset: -1) }.should.raise(ArgumentError, "offset can't be negative")
+      end
+    end
   end
 
   it "returns nil if the offset is at the end of the string" do
@@ -29,6 +43,19 @@ describe "String#unpack1" do
   end
 
   it "raises an ArgumentError when the offset is larger than the string bytesize" do
-    -> { "a".unpack1("C", offset: 2) }.should raise_error(ArgumentError, "offset outside of string")
+    -> { "a".unpack1("C", offset: 2) }.should.raise(ArgumentError, "offset outside of string")
+  end
+
+  context "with format 'm0'" do
+    # unpack1("m0") takes a special code path that calls Pack.unpackBase46Strict instead of Pack.unpack_m,
+    # which is why we repeat the tests for unpack("m0") here.
+
+    it "decodes base64" do
+      "dGVzdA==".unpack1("m0").should == "test"
+    end
+
+    it "raises an ArgumentError for an invalid base64 character" do
+      -> { "dGV%zdA==".unpack1("m0") }.should.raise(ArgumentError)
+    end
   end
 end