diff --git a/CHANGELOG.md b/CHANGELOG.md
index 54b5f09..0afa76e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+- Add a basic benchmark file
+- Add standardRB badge
+- Add `.freeze` on `CONST` lookup objects
+- Remove unused `@mode` instance variable
+- A batch of small refactors and optimizations
+
 ## [1.0.0] - 2021-04-23
 
 ### Changed
diff --git a/README.md b/README.md
index ba328ca..efe1e14 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,5 @@
 ![](https://github.com/whomwah/rqrcode_core/actions/workflows/ruby.yml/badge.svg)
+[![Ruby Style Guide](https://img.shields.io/badge/code_style-standard-brightgreen.svg)](https://github.com/testdouble/standard)
 
 # RQRCodeCore
 
diff --git a/Rakefile b/Rakefile
index ba9e2c1..c71f017 100644
--- a/Rakefile
+++ b/Rakefile
@@ -9,6 +9,11 @@ begin
   end
 
   task default: [:test, "standard:fix"]
+
+  desc "Run a simple benchmark (x1000)"
+  task :benchmark do
+    ruby "test/benchmark.rb"
+  end
 rescue LoadError
   # no standard/rspec available
 end
diff --git a/lib/rqrcode_core/qrcode/qr_8bit_byte.rb b/lib/rqrcode_core/qrcode/qr_8bit_byte.rb
index 706b32f..320fb1f 100644
--- a/lib/rqrcode_core/qrcode/qr_8bit_byte.rb
+++ b/lib/rqrcode_core/qrcode/qr_8bit_byte.rb
@@ -2,19 +2,13 @@
 
 module RQRCodeCore
   class QR8bitByte
-    attr_reader :mode
-
     def initialize(data)
-      @mode = QRMODE[:mode_8bit_byte]
       @data = data
     end
 
-    def get_length
-      @data.bytesize
-    end
-
     def write(buffer)
-      buffer.byte_encoding_start(get_length)
+      buffer.byte_encoding_start(@data.bytesize)
+
       @data.each_byte do |b|
         buffer.put(b, 8)
       end
diff --git a/lib/rqrcode_core/qrcode/qr_alphanumeric.rb b/lib/rqrcode_core/qrcode/qr_alphanumeric.rb
index e948a12..c7b97dd 100644
--- a/lib/rqrcode_core/qrcode/qr_alphanumeric.rb
+++ b/lib/rqrcode_core/qrcode/qr_alphanumeric.rb
@@ -1,32 +1,27 @@
 # frozen_string_literal: true
 
 module RQRCodeCore
-  ALPHANUMERIC = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", " ", "$", "%", "*", "+", "-", ".", "/", ":"]
+  ALPHANUMERIC = [
+    "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F", "G", "H", "I",
+    "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", " ", "$",
+    "%", "*", "+", "-", ".", "/", ":"
+  ].freeze
 
   class QRAlphanumeric
-    attr_reader :mode
-
     def initialize(data)
-      @mode = QRMODE[:mode_alpha_numk]
-
-      raise QRCodeArgumentError, "Not a alpha numeric uppercase string `#{data}`" unless QRAlphanumeric.valid_data?(data)
+      unless QRAlphanumeric.valid_data?(data)
+        raise QRCodeArgumentError, "Not a alpha numeric uppercase string `#{data}`"
+      end
 
       @data = data
     end
 
-    def get_length
-      @data.size
-    end
-
-    def self.valid_data? data
-      data.each_char do |s|
-        return false if ALPHANUMERIC.index(s).nil?
-      end
-      true
+    def self.valid_data?(data)
+      (data.chars - ALPHANUMERIC).empty?
     end
 
     def write(buffer)
-      buffer.alphanumeric_encoding_start(get_length)
+      buffer.alphanumeric_encoding_start(@data.size)
 
       @data.size.times do |i|
         if i % 2 == 0
diff --git a/lib/rqrcode_core/qrcode/qr_bit_buffer.rb b/lib/rqrcode_core/qrcode/qr_bit_buffer.rb
index e71fae1..1aa29fc 100644
--- a/lib/rqrcode_core/qrcode/qr_bit_buffer.rb
+++ b/lib/rqrcode_core/qrcode/qr_bit_buffer.rb
@@ -64,8 +64,8 @@ def pad_until(prefered_size)
 
       # Pad with padding code words
       while get_length_in_bits < prefered_size
-        put(QRBitBuffer::PAD0, 8)
-        put(QRBitBuffer::PAD1, 8) if get_length_in_bits < prefered_size
+        put(PAD0, 8)
+        put(PAD1, 8) if get_length_in_bits < prefered_size
       end
     end
 
diff --git a/lib/rqrcode_core/qrcode/qr_code.rb b/lib/rqrcode_core/qrcode/qr_code.rb
index 510e7a3..9777ddb 100644
--- a/lib/rqrcode_core/qrcode/qr_code.rb
+++ b/lib/rqrcode_core/qrcode/qr_code.rb
@@ -5,20 +5,20 @@ module RQRCodeCore
     mode_number: 1 << 0,
     mode_alpha_numk: 1 << 1,
     mode_8bit_byte: 1 << 2
-  }
+  }.freeze
 
   QRMODE_NAME = {
     number: :mode_number,
     alphanumeric: :mode_alpha_numk,
     byte_8bit: :mode_8bit_byte
-  }
+  }.freeze
 
   QRERRORCORRECTLEVEL = {
     l: 1,
     m: 0,
     q: 3,
     h: 2
-  }
+  }.freeze
 
   QRMASKPATTERN = {
     pattern000: 0,
@@ -29,7 +29,7 @@ module RQRCodeCore
     pattern101: 5,
     pattern110: 6,
     pattern111: 7
-  }
+  }.freeze
 
   QRMASKCOMPUTATIONS = [
     proc { |i, j| (i + j) % 2 == 0 },
@@ -40,7 +40,7 @@ module RQRCodeCore
     proc { |i, j| (i * j) % 2 + (i * j) % 3 == 0 },
     proc { |i, j| ((i * j) % 2 + (i * j) % 3) % 2 == 0 },
     proc { |i, j| ((i * j) % 3 + (i + j) % 2) % 2 == 0 }
-  ]
+  ].freeze
 
   QRPOSITIONPATTERNLENGTH = (7 + 1) * 2 + 1
   QRFORMATINFOLENGTH = 15
@@ -132,7 +132,7 @@ module RQRCodeCore
         790, 842, 898, 958, 983, 1051, 1093, 1139, 1219, 1273
       ]
     }
-  }
+  }.freeze
 
   # StandardErrors
 
@@ -314,7 +314,7 @@ def make #:nodoc:
 
     private
 
-    def prepare_common_patterns
+    def prepare_common_patterns #:nodoc:
       @modules.map! { |row| Array.new(@module_count) }
 
       place_position_probe_pattern(0, 0)
@@ -490,7 +490,7 @@ def extract_options!(arr) #:nodoc:
     end
 
     class << self
-      def count_max_data_bits(rs_blocks)
+      def count_max_data_bits(rs_blocks) #:nodoc:
         max_data_bytes = rs_blocks.reduce(0) do |sum, rs_block|
           sum + rs_block.data_count
         end
diff --git a/lib/rqrcode_core/qrcode/qr_math.rb b/lib/rqrcode_core/qrcode/qr_math.rb
index 3ff10c9..de24c8b 100644
--- a/lib/rqrcode_core/qrcode/qr_math.rb
+++ b/lib/rqrcode_core/qrcode/qr_math.rb
@@ -21,8 +21,8 @@ class QRMath
         log_table[exp_table[i]] = i
       end
 
-      const_set(:EXP_TABLE, exp_table)
-      const_set(:LOG_TABLE, log_table)
+      const_set(:EXP_TABLE, exp_table).freeze
+      const_set(:LOG_TABLE, log_table).freeze
     }
 
     class << self
diff --git a/lib/rqrcode_core/qrcode/qr_numeric.rb b/lib/rqrcode_core/qrcode/qr_numeric.rb
index ef6d980..83eb460 100644
--- a/lib/rqrcode_core/qrcode/qr_numeric.rb
+++ b/lib/rqrcode_core/qrcode/qr_numeric.rb
@@ -1,32 +1,21 @@
 # frozen_string_literal: true
 
 module RQRCodeCore
-  NUMERIC = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"].freeze
+  NUMERIC = %w[0 1 2 3 4 5 6 7 8 9].freeze
 
   class QRNumeric
-    attr_reader :mode
-
     def initialize(data)
-      @mode = QRMODE[:mode_number]
-
       raise QRCodeArgumentError, "Not a numeric string `#{data}`" unless QRNumeric.valid_data?(data)
 
       @data = data
     end
 
-    def get_length
-      @data.size
-    end
-
-    def self.valid_data? data
-      data.each_char do |s|
-        return false if NUMERIC.index(s).nil?
-      end
-      true
+    def self.valid_data?(data)
+      (data.chars - NUMERIC).empty?
     end
 
     def write(buffer)
-      buffer.numeric_encoding_start(get_length)
+      buffer.numeric_encoding_start(@data.size)
 
       @data.size.times do |i|
         if i % 3 == 0
diff --git a/lib/rqrcode_core/qrcode/qr_rs_block.rb b/lib/rqrcode_core/qrcode/qr_rs_block.rb
index 8797bae..15d35a5 100644
--- a/lib/rqrcode_core/qrcode/qr_rs_block.rb
+++ b/lib/rqrcode_core/qrcode/qr_rs_block.rb
@@ -10,7 +10,7 @@ def initialize(total_count, data_count)
     end
 
     # http://www.thonky.com/qr-code-tutorial/error-correction-table/
-    RQRCodeCore::QRRSBlock::RS_BLOCK_TABLE = [
+    RS_BLOCK_TABLE = [
       # L
       # M
       # Q
@@ -256,7 +256,7 @@ def initialize(total_count, data_count)
       [34, 54, 24, 34, 55, 25],
       [20, 45, 15, 61, 46, 16]
 
-    ]
+    ].freeze
 
     def self.get_rs_blocks(version, error_correct_level)
       rs_block = QRRSBlock.get_rs_block_table(version, error_correct_level)
diff --git a/lib/rqrcode_core/qrcode/qr_util.rb b/lib/rqrcode_core/qrcode/qr_util.rb
index 89e0575..5522da2 100644
--- a/lib/rqrcode_core/qrcode/qr_util.rb
+++ b/lib/rqrcode_core/qrcode/qr_util.rb
@@ -43,7 +43,7 @@ class QRUtil
       [6, 32, 58, 84, 110, 136, 162],
       [6, 26, 54, 82, 110, 138, 166],
       [6, 30, 58, 86, 114, 142, 170]
-    ]
+    ].freeze
 
     G15 = 1 << 10 | 1 << 8 | 1 << 5 | 1 << 4 | 1 << 2 | 1 << 1 | 1 << 0
     G18 = 1 << 12 | 1 << 11 | 1 << 10 | 1 << 9 | 1 << 8 | 1 << 5 | 1 << 2 | 1 << 0
@@ -59,7 +59,7 @@ class QRUtil
       QRMODE[:mode_alpha_numk] => [9, 11, 13],
       QRMODE[:mode_8bit_byte] => [8, 16, 16],
       QRMODE[:mode_kanji] => [8, 10, 12]
-    }
+    }.freeze
 
     def self.max_size
       PATTERN_POSITION_TABLE.count
diff --git a/test/benchmark.rb b/test/benchmark.rb
new file mode 100644
index 0000000..680ea23
--- /dev/null
+++ b/test/benchmark.rb
@@ -0,0 +1,11 @@
+$LOAD_PATH.unshift File.expand_path("../../lib", __FILE__)
+require "rqrcode_core"
+require "benchmark"
+
+Benchmark.bm do |benchmark|
+  benchmark.report("RQRCode") do
+    1000.times do
+      RQRCodeCore::QRCode.new("https://kyan.com").to_s
+    end
+  end
+end
diff --git a/test/rqrcode_core/data.rb b/test/rqrcode_core/data.rb
index 5417c73..c814431 100644
--- a/test/rqrcode_core/data.rb
+++ b/test/rqrcode_core/data.rb
@@ -21,5 +21,3 @@
 MATRIX_4_Q = [[true, true, true, true, true, true, true, false, false, true, true, true, false, true, true, true, false, true, true, false, false, true, true, false, true, false, true, true, true, true, true, true, true], [true, false, false, false, false, false, true, false, true, false, false, true, false, false, false, true, true, false, true, true, false, false, false, false, false, false, true, false, false, false, false, false, true], [true, false, true, true, true, false, true, false, false, false, true, true, true, false, true, false, false, false, false, true, true, true, false, true, true, false, true, false, true, true, true, false, true], [true, false, true, true, true, false, true, false, true, false, false, false, true, true, true, false, true, false, true, true, true, false, true, true, true, false, true, false, true, true, true, false, true], [true, false, true, true, true, false, true, false, true, false, true, true, false, false, true, true, false, false, false, false, false, false, true, true, false, false, true, false, true, true, true, false, true], [true, false, false, false, false, false, true, false, false, true, true, false, true, true, false, true, false, true, false, true, false, true, false, false, true, false, true, false, false, false, false, false, true], [true, true, true, true, true, true, true, false, true, false, true, false, true, false, true, false, true, false, true, false, true, false, true, false, true, false, true, true, true, true, true, true, true], [false, false, false, false, false, false, false, false, true, true, false, true, true, true, true, false, false, false, false, false, false, false, true, true, false, false, false, false, false, false, false, false, false], [false, true, false, true, true, true, true, false, true, false, false, false, true, true, false, false, true, true, false, false, false, false, false, true, true, true, true, false, true, true, false, true, false], [false, false, false, true, true, true, false, false, true, true, false, false, true, false, false, true, false, true, true, true, false, true, false, true, false, false, false, false, true, true, true, false, false], [true, false, false, false, true, false, true, false, true, false, true, false, true, true, true, false, true, false, false, false, false, false, true, true, false, false, true, false, true, false, false, true, true], [false, false, false, true, true, false, false, false, false, true, false, false, true, false, true, false, false, false, true, false, false, true, true, true, false, false, true, false, true, false, true, true, true], [true, true, true, false, false, true, true, true, false, true, true, false, true, false, false, true, true, true, false, true, false, true, false, true, false, false, true, true, false, false, false, false, false], [true, false, false, false, true, false, false, false, true, false, false, true, true, false, false, true, false, false, true, true, true, false, false, false, true, true, false, true, false, false, true, false, false], [true, false, true, false, true, true, true, true, false, false, false, false, true, false, true, false, true, true, true, true, true, true, true, false, false, false, true, true, true, false, false, false, false], [true, false, true, true, false, false, false, false, false, true, true, true, true, false, false, false, true, false, false, false, true, false, true, false, true, false, false, false, true, false, true, true, false], [false, false, true, false, false, false, true, false, true, false, true, false, false, true, true, true, false, true, true, false, true, false, true, true, false, true, true, true, true, false, false, true, true], [true, true, false, false, true, false, false, true, false, true, true, false, false, true, false, true, false, true, false, true, true, false, false, false, false, false, true, true, true, false, true, false, true], [true, false, true, true, true, true, true, true, true, false, false, false, true, true, true, false, true, false, false, true, true, true, true, true, true, false, false, true, false, false, false, true, true], [true, false, false, false, true, true, false, false, true, true, false, true, false, false, false, true, true, true, true, false, true, false, true, true, false, true, true, false, false, false, true, false, false], [true, false, true, true, false, true, true, false, true, false, true, true, false, false, false, true, true, true, false, true, false, true, true, true, true, false, false, false, false, false, false, true, false], [true, false, true, false, true, true, false, false, false, true, false, false, false, true, false, false, true, false, true, false, false, false, false, false, false, true, false, false, true, false, true, true, false], [true, false, false, false, true, false, true, false, true, true, false, true, false, false, false, true, true, false, true, true, true, false, false, false, true, false, true, false, false, true, true, true, true], [true, false, false, false, false, false, false, false, true, false, false, false, false, true, true, false, false, true, true, true, true, false, true, false, false, true, true, false, false, true, true, true, false], [true, true, true, false, false, true, true, false, true, true, false, false, true, true, false, false, false, false, true, false, false, false, false, false, true, true, true, true, true, false, false, true, true], [false, false, false, false, false, false, false, false, true, true, false, false, true, false, true, true, true, false, false, false, false, true, false, false, true, false, false, false, true, true, false, false, false], [true, true, true, true, true, true, true, false, false, true, false, true, true, true, true, true, true, false, true, true, true, false, false, true, true, false, true, false, true, false, false, false, false], [true, false, false, false, false, false, true, false, true, true, false, true, true, true, false, false, true, false, false, true, false, true, true, false, true, false, false, false, true, true, true, true, true], [true, false, true, true, true, false, true, false, true, false, true, true, false, false, false, false, true, false, true, false, false, true, true, true, true, true, true, true, true, true, false, true, true], [true, false, true, true, true, false, true, false, true, true, false, false, true, true, true, false, true, false, true, false, false, true, true, false, false, true, false, false, false, true, true, false, true], [true, false, true, true, true, false, true, false, false, true, true, false, true, true, false, false, true, true, true, true, false, false, false, false, false, true, false, false, true, true, true, true, true], [true, false, false, false, false, false, true, false, true, true, false, false, true, false, false, true, false, true, false, true, true, false, true, false, true, false, true, false, true, false, true, true, true], [true, true, true, true, true, true, true, false, false, true, true, false, true, true, true, false, true, false, true, true, false, false, false, false, true, false, true, true, true, true, false, false, false]]
 
 MATRIX_UTF8_RU_TEST = [[true, true, true, true, true, true, true, false, true, false, true, true, true, true, true, false, false, false, true, true, true, true, true, true, true], [true, false, false, false, false, false, true, false, false, false, false, false, true, true, true, true, true, false, true, false, false, false, false, false, true], [true, false, true, true, true, false, true, false, true, false, false, true, false, true, true, true, true, false, true, false, true, true, true, false, true], [true, false, true, true, true, false, true, false, false, false, true, false, true, true, false, true, true, false, true, false, true, true, true, false, true], [true, false, true, true, true, false, true, false, true, false, false, true, true, true, false, true, false, false, true, false, true, true, true, false, true], [true, false, false, false, false, false, true, false, false, true, false, false, true, true, false, true, false, false, true, false, false, false, false, false, true], [true, true, true, true, true, true, true, false, true, false, true, false, true, false, true, false, true, false, true, true, true, true, true, true, true], [false, false, false, false, false, false, false, false, true, true, true, false, false, false, false, true, true, false, false, false, false, false, false, false, false], [false, false, false, false, false, true, true, false, false, false, true, false, true, true, false, true, false, false, true, false, true, false, true, false, true], [false, false, false, false, false, true, false, true, true, true, true, true, false, true, true, true, false, false, true, true, false, false, true, true, true], [false, true, true, false, true, true, true, false, false, false, false, false, false, true, false, false, false, false, true, false, true, true, false, true, false], [true, true, false, false, true, false, false, false, false, false, true, false, false, false, false, true, false, true, true, true, true, false, true, false, false], [false, false, false, false, false, false, true, true, false, false, false, false, true, true, false, false, false, true, true, true, true, false, false, true, true], [true, true, true, true, false, true, false, false, false, true, false, true, false, false, true, false, false, true, true, false, false, true, false, false, true], [true, false, false, true, true, false, true, true, true, false, false, true, true, true, false, true, true, true, false, false, true, false, false, false, false], [true, false, false, false, false, false, false, false, true, true, false, false, false, true, false, false, true, false, false, false, true, true, false, true, true], [true, false, true, true, true, true, true, true, false, false, true, false, false, true, true, true, true, true, true, true, true, false, false, false, true], [false, false, false, false, false, false, false, false, true, false, false, false, false, true, true, false, true, false, false, false, true, false, false, true, true], [true, true, true, true, true, true, true, false, false, true, true, true, false, true, false, true, true, false, true, false, true, false, true, false, false], [true, false, false, false, false, false, true, false, true, true, false, false, true, false, true, true, true, false, false, false, true, false, true, false, true], [true, false, true, true, true, false, true, false, false, true, false, true, true, false, false, false, true, true, true, true, true, true, false, false, false], [true, false, true, true, true, false, true, false, false, true, true, true, true, true, false, false, false, true, false, false, true, false, true, false, true], [true, false, true, true, true, false, true, false, false, true, false, false, false, true, false, false, true, false, true, false, true, false, false, false, true], [true, false, false, false, false, false, true, false, false, true, false, false, false, false, true, true, false, false, true, true, false, true, true, false, true], [true, true, true, true, true, true, true, false, false, true, false, true, false, false, false, true, true, false, true, true, true, false, true, false, true]]
-
-AS_ANSI = "\e[47m                                                          \e[m\n\e[47m                                                          \e[m\n\e[47m                                                          \e[m\n\e[47m                                                          \e[m\n\e[47m        \e[40m              \e[47m  \e[40m      \e[47m      \e[40m              \e[47m        \e[m\n\e[47m        \e[40m  \e[47m          \e[40m  \e[47m  \e[40m  \e[47m          \e[40m  \e[47m          \e[40m  \e[47m        \e[m\n\e[47m        \e[40m  \e[47m  \e[40m      \e[47m  \e[40m  \e[47m  \e[40m  \e[47m  \e[40m    \e[47m    \e[40m  \e[47m  \e[40m      \e[47m  \e[40m  \e[47m        \e[m\n\e[47m        \e[40m  \e[47m  \e[40m      \e[47m  \e[40m  \e[47m    \e[40m        \e[47m  \e[40m  \e[47m  \e[40m      \e[47m  \e[40m  \e[47m        \e[m\n\e[47m        \e[40m  \e[47m  \e[40m      \e[47m  \e[40m  \e[47m          \e[40m  \e[47m  \e[40m  \e[47m  \e[40m      \e[47m  \e[40m  \e[47m        \e[m\n\e[47m        \e[40m  \e[47m          \e[40m  \e[47m  \e[40m    \e[47m        \e[40m  \e[47m          \e[40m  \e[47m        \e[m\n\e[47m        \e[40m              \e[47m  \e[40m  \e[47m  \e[40m  \e[47m  \e[40m  \e[47m  \e[40m              \e[47m        \e[m\n\e[47m                        \e[40m      \e[47m                            \e[m\n\e[47m            \e[40m      \e[47m  \e[40m  \e[47m  \e[40m      \e[47m  \e[40m        \e[47m    \e[40m      \e[47m        \e[m\n\e[47m            \e[40m  \e[47m  \e[40m    \e[47m    \e[40m  \e[47m      \e[40m    \e[47m  \e[40m  \e[47m  \e[40m  \e[47m    \e[40m  \e[47m        \e[m\n\e[47m        \e[40m        \e[47m  \e[40m    \e[47m  \e[40m    \e[47m  \e[40m      \e[47m    \e[40m  \e[47m    \e[40m  \e[47m          \e[m\n\e[47m            \e[40m  \e[47m    \e[40m  \e[47m    \e[40m  \e[47m  \e[40m                    \e[47m          \e[m\n\e[47m              \e[40m  \e[47m  \e[40m    \e[47m                  \e[40m    \e[47m              \e[m\n\e[47m                        \e[40m  \e[47m  \e[40m  \e[47m  \e[40m  \e[47m          \e[40m  \e[47m  \e[40m  \e[47m        \e[m\n\e[47m        \e[40m              \e[47m      \e[40m      \e[47m    \e[40m  \e[47m  \e[40m  \e[47m  \e[40m  \e[47m          \e[m\n\e[47m        \e[40m  \e[47m          \e[40m  \e[47m    \e[40m  \e[47m  \e[40m  \e[47m    \e[40m  \e[47m    \e[40m    \e[47m            \e[m\n\e[47m        \e[40m  \e[47m  \e[40m      \e[47m  \e[40m  \e[47m  \e[40m  \e[47m  \e[40m    \e[47m    \e[40m    \e[47m      \e[40m  \e[47m          \e[m\n\e[47m        \e[40m  \e[47m  \e[40m      \e[47m  \e[40m  \e[47m  \e[40m    \e[47m  \e[40m  \e[47m  \e[40m  \e[47m  \e[40m  \e[47m                  \e[m\n\e[47m        \e[40m  \e[47m  \e[40m      \e[47m  \e[40m  \e[47m  \e[40m    \e[47m    \e[40m  \e[47m  \e[40m  \e[47m  \e[40m      \e[47m            \e[m\n\e[47m        \e[40m  \e[47m          \e[40m  \e[47m      \e[40m    \e[47m      \e[40m    \e[47m  \e[40m  \e[47m            \e[m\n\e[47m        \e[40m              \e[47m              \e[40m  \e[47m  \e[40m  \e[47m  \e[40m    \e[47m          \e[m\n\e[47m                                                          \e[m\n\e[47m                                                          \e[m\n\e[47m                                                          \e[m\n\e[47m                                                          \e[m\n"
diff --git a/test/rqrcode_core/rqrcode_test.rb b/test/rqrcode_core/rqrcode_test.rb
index 5144822..61c54b3 100644
--- a/test/rqrcode_core/rqrcode_test.rb
+++ b/test/rqrcode_core/rqrcode_test.rb
@@ -81,6 +81,14 @@ def test_auto_alphanumeric
     assert_equal "xxxxxxx xxx   xxxxxxx\n", qr.to_s[0..21]
   end
 
+  def test_manual_alphanumeric
+    assert_equal :mode_alpha_numk, RQRCodeCore::QRCode.new("DUNCAN", mode: :alphanumeric).mode
+
+    assert_raises(RQRCodeCore::QRCodeArgumentError) {
+      RQRCodeCore::QRCode.new("Duncan", mode: :alphanumeric)
+    }
+  end
+
   def test_auto_numeric
     # When digit only automatically uses numeric mode, default ecc level is :h
     digits = RQRCodeCore::QRCode.new("1" * 17) # Version 1, numeric mode, ECC h