Add specs for IO#read_bytes with converter (#16250)

Author: straight-shoota

spec/std/io/byte_format_spec.cr

@@ -19,6 +19,12 @@ private def new_string_io(*bytes)
   io
 end
 
+private module ReadBytesConverter
+  def self.from_io(io : IO, format = IO::ByteFormat::NetworkEndian) : Int32
+    io.read_bytes(Int32, format: format)
+  end
+end
+
 describe IO::ByteFormat do
   describe "little endian" do
     describe "encode" do
@@ -130,6 +136,11 @@ describe IO::ByteFormat do
           float = io.read_bytes Float64, IO::ByteFormat::LittleEndian
           float.should be_close(1.234, 0.0001)
         end
+
+        it "reads with converter" do
+          io = new_string_io(0x78, 0x56, 0x34, 0x12)
+          io.read_bytes(ReadBytesConverter, IO::ByteFormat::LittleEndian).should eq 0x12345678_i32
+        end
       end
 
       describe "from slice" do
@@ -248,6 +259,11 @@ describe IO::ByteFormat do
           float = io.read_bytes Float64, IO::ByteFormat::BigEndian
           float.should be_close(1.234, 0.0001)
         end
+
+        it "reads with converter" do
+          io = new_string_io(0x12, 0x34, 0x56, 0x78)
+          io.read_bytes(ReadBytesConverter, IO::ByteFormat::BigEndian).should eq 0x12345678_i32
+        end
       end
 
       describe "from slice" do