1 files changed, 26 insertions, 0 deletions
diff --git a/spec/ruby/core/string/unpack1_spec.rb b/spec/ruby/core/string/unpack1_spec.rb
index 5fe81733fb..df830916a3 100644
--- a/spec/ruby/core/string/unpack1_spec.rb
+++ b/spec/ruby/core/string/unpack1_spec.rb
@@ -7,4 +7,30 @@ describe "String#unpack1" do
     "aG9nZWZ1Z2E=".unpack1("m").should == "hogefuga"
     "A".unpack1("B*").should == "01000001"
   end
+
+  ruby_version_is "3.1" do
+    it "starts unpacking from the given offset" do
+      "ZZABCD".unpack1('x3C', offset: 2).should == "ABCD".unpack('x3C')[0]
+      "ZZZZaG9nZWZ1Z2E=".unpack1("m", offset: 4).should == "hogefuga"
+      "ZA".unpack1("B*", offset: 1).should == "01000001"
+    end
+
+    it "traits offset as a bytes offset" do
+      "؈".unpack("CC").should == [216, 136]
+      "؈".unpack1("C").should == 216
+      "؈".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")
+    end
+
+    it "returns nil if the offset is at the end of the string" do
+      "a".unpack1("C", offset: 1).should == nil
+    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")
+    end
+  end
 end