From 0673e2514a1c1480a0d24546b11c18237ec7ab03 Mon Sep 17 00:00:00 2001
From: Sutou Kouhei <kou@clear-code.com>
Date: Wed, 22 Jul 2026 11:53:24 +0900
Subject: [PATCH] GH-50588: [Ruby] Add `ArrowFormat::Array#[]`

---
 .../lib/arrow-format/array.rb                 | 46 +++++++++++++++++++
 .../lib/arrow-format/error.rb                 |  1 +
 .../red-arrow-format/lib/arrow-format/type.rb |  1 +
 .../test/test-binary-array.rb                 | 15 ++++++
 .../test/test-boolean-array.rb                | 15 ++++++
 .../test/test-date32-array.rb                 | 12 +++++
 .../test/test-date64-array.rb                 | 12 +++++
 .../test/test-day-time-interval-array.rb      | 19 ++++++++
 .../test/test-duration-array.rb               | 15 ++++++
 .../test/test-float32-array.rb                | 15 ++++++
 .../test/test-float64-array.rb                | 15 ++++++
 .../red-arrow-format/test/test-int16-array.rb | 15 ++++++
 .../red-arrow-format/test/test-int32-array.rb | 15 ++++++
 .../red-arrow-format/test/test-int64-array.rb | 15 ++++++
 ruby/red-arrow-format/test/test-int8-array.rb | 15 ++++++
 .../test/test-large-binary-array.rb           | 15 ++++++
 .../test/test-large-utf8-array.rb             | 15 ++++++
 .../test-month-day-nano-interval-array.rb     | 19 ++++++++
 ruby/red-arrow-format/test/test-null-array.rb |  8 ++++
 .../test/test-time32-array.rb                 | 12 +++++
 .../test/test-time64-array.rb                 | 12 +++++
 .../test/test-timestamp-array.rb              | 16 +++++++
 .../test/test-uint16-array.rb                 | 15 ++++++
 .../test/test-uint32-array.rb                 | 15 ++++++
 .../test/test-uint64-array.rb                 | 15 ++++++
 .../red-arrow-format/test/test-uint8-array.rb | 15 ++++++
 ruby/red-arrow-format/test/test-utf8-array.rb | 15 ++++++
 .../test/test-year-month-interval-array.rb    | 15 ++++++
 28 files changed, 413 insertions(+)

diff --git a/ruby/red-arrow-format/lib/arrow-format/array.rb b/ruby/red-arrow-format/lib/arrow-format/array.rb
index 0a25ebf6b3ba..d190cc29923e 100644
--- a/ruby/red-arrow-format/lib/arrow-format/array.rb
+++ b/ruby/red-arrow-format/lib/arrow-format/array.rb
@@ -61,6 +61,14 @@ def null?(i)
       not valid?(i)
     end
 
+    def [](i)
+      if valid?(i)
+        unpack_value(i)
+      else
+        nil
+      end
+    end
+
     def n_nulls
       if @validity_buffer.nil?
         0
@@ -167,6 +175,14 @@ def initialize(size)
       super(NullType.singleton, size, nil)
     end
 
+    def valid?(i)
+      false
+    end
+
+    def null?(i)
+      true
+    end
+
     def each_buffer
       return to_enum(__method__) unless block_given?
     end
@@ -294,6 +310,11 @@ def pack_value(value, template, type)
       value = 0 if value.nil?
       [value].pack(template)
     end
+
+    def unpack_value(i)
+      offset = element_size * (@offset + i)
+      @values_buffer.get_value(@type.buffer_type, offset)
+    end
   end
 
   class BooleanArray < PrimitiveArray
@@ -362,6 +383,10 @@ def build_data(data, type)
       validity_buffer = validity_buffer_builder&.finish(n)
       return n, validity_buffer, values_buffer_builder.finish
     end
+
+    def unpack_value(i)
+      values_bitmap[i]
+    end
   end
 
   class IntArray < PrimitiveArray
@@ -600,6 +625,11 @@ def pack_value(value, template, type)
         value.pack(template)
       end
     end
+
+    def unpack_value(i)
+      offset = element_size * (@offset + i)
+      @values_buffer.get_values([@type.buffer_type] * 2, offset)
+    end
   end
 
   class MonthDayNanoIntervalArray < IntervalArray
@@ -661,6 +691,13 @@ def pack_value(value, template, type)
         value.pack(template)
       end
     end
+
+    def unpack_value(i)
+      buffer_types = @type.buffer_types
+      value_size = IO::Buffer.size_of(buffer_types)
+      offset = value_size * (@offset + i)
+      @values_buffer.get_values(buffer_types, offset)
+    end
   end
 
   class DurationArray < TemporalArray
@@ -768,6 +805,15 @@ def build_data(data)
     def offset_size
       IO::Buffer.size_of(@type.offset_buffer_type)
     end
+
+    def unpack_value(i)
+      offset_types = [@type.offset_buffer_type] * 2
+      offsets_offset = offset_size * (@offset + i)
+      offset, next_offset = @offsets_buffer.get_values(offset_types,
+                                                       offsets_offset)
+      length = next_offset - offset
+      @values_buffer.get_string(offset, length, @type.encoding)
+    end
   end
 
   class BinaryArray < VariableSizeBinaryArray
diff --git a/ruby/red-arrow-format/lib/arrow-format/error.rb b/ruby/red-arrow-format/lib/arrow-format/error.rb
index f6aebb364552..b82d10e2ae46 100644
--- a/ruby/red-arrow-format/lib/arrow-format/error.rb
+++ b/ruby/red-arrow-format/lib/arrow-format/error.rb
@@ -1,3 +1,4 @@
+# Licensed to the Apache Software Foundation (ASF) under one
 # or more contributor license agreements.  See the NOTICE file
 # distributed with this work for additional information
 # regarding copyright ownership.  The ASF licenses this file
diff --git a/ruby/red-arrow-format/lib/arrow-format/type.rb b/ruby/red-arrow-format/lib/arrow-format/type.rb
index 4ba989515e8f..b52136769d47 100644
--- a/ruby/red-arrow-format/lib/arrow-format/type.rb
+++ b/ruby/red-arrow-format/lib/arrow-format/type.rb
@@ -1,3 +1,4 @@
+# Licensed to the Apache Software Foundation (ASF) under one
 # or more contributor license agreements.  See the NOTICE file
 # distributed with this work for additional information
 # regarding copyright ownership.  The ASF licenses this file
diff --git a/ruby/red-arrow-format/test/test-binary-array.rb b/ruby/red-arrow-format/test/test-binary-array.rb
index bcc122ccb042..78783b7996b7 100644
--- a/ruby/red-arrow-format/test/test-binary-array.rb
+++ b/ruby/red-arrow-format/test/test-binary-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestBinaryArray < Test::Unit::TestCase
+  def setup
+    @values = ["\x00\x01".b, nil, "\xff\x10".b]
+    @array = ArrowFormat::BinaryArray.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = ["\x00\x01".b, "\xff\x10".b]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-boolean-array.rb b/ruby/red-arrow-format/test/test-boolean-array.rb
index 36a3c53dafc8..d5357b081ca9 100644
--- a/ruby/red-arrow-format/test/test-boolean-array.rb
+++ b/ruby/red-arrow-format/test/test-boolean-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestBooleanArray < Test::Unit::TestCase
+  def setup
+    @values = [true, nil, false]
+    @array = ArrowFormat::BooleanArray.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       assert_equal([true, false],
@@ -53,4 +58,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-date32-array.rb b/ruby/red-arrow-format/test/test-date32-array.rb
index ee9b95df3cab..ef98b8d902f7 100644
--- a/ruby/red-arrow-format/test/test-date32-array.rb
+++ b/ruby/red-arrow-format/test/test-date32-array.rb
@@ -19,6 +19,8 @@ class TestDate32Array < Test::Unit::TestCase
   def setup
     @date_2017_08_28 = 17406
     @date_2025_12_09 = 20431
+    @values = [@date_2017_08_28, nil, @date_2025_12_09]
+    @array = ArrowFormat::Date32Array.new(@values)
   end
 
   sub_test_case("#initialize") do
@@ -57,4 +59,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-date64-array.rb b/ruby/red-arrow-format/test/test-date64-array.rb
index 5dcbdfc2cd66..167911fe1cd3 100644
--- a/ruby/red-arrow-format/test/test-date64-array.rb
+++ b/ruby/red-arrow-format/test/test-date64-array.rb
@@ -19,6 +19,8 @@ class TestDate64Array < Test::Unit::TestCase
   def setup
     @date_2017_08_28_00_00_00 = 1503878400000
     @date_2025_12_10_00_00_00 = 1765324800000
+    @values = [@date_2017_08_28_00_00_00, nil, @date_2025_12_10_00_00_00]
+    @array = ArrowFormat::Date64Array.new(@values)
   end
 
   sub_test_case("#initialize") do
@@ -57,4 +59,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-day-time-interval-array.rb b/ruby/red-arrow-format/test/test-day-time-interval-array.rb
index 477dde7cba88..b7151190cda4 100644
--- a/ruby/red-arrow-format/test/test-day-time-interval-array.rb
+++ b/ruby/red-arrow-format/test/test-day-time-interval-array.rb
@@ -16,6 +16,15 @@
 # under the License.
 
 class TestDayTimeIntervalArray < Test::Unit::TestCase
+  def setup
+    @values = [
+      [1, 100],
+      nil,
+      [3, 300],
+    ]
+    @array = ArrowFormat::DayTimeIntervalArray.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [
@@ -85,4 +94,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-duration-array.rb b/ruby/red-arrow-format/test/test-duration-array.rb
index 92362c2e4d89..24d0bd98a0b8 100644
--- a/ruby/red-arrow-format/test/test-duration-array.rb
+++ b/ruby/red-arrow-format/test/test-duration-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestDurationArray < Test::Unit::TestCase
+  def setup
+    @values = [-(2 ** 63), nil, (2 ** 63) - 1]
+    @array = ArrowFormat::DurationArray.new(:second, @values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [-(2 ** 63), (2 ** 63) - 1]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-float32-array.rb b/ruby/red-arrow-format/test/test-float32-array.rb
index 1769bb2d3fbb..243c46b23507 100644
--- a/ruby/red-arrow-format/test/test-float32-array.rb
+++ b/ruby/red-arrow-format/test/test-float32-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestFloat32Array < Test::Unit::TestCase
+  def setup
+    @values = [-Float::INFINITY, nil, +Float::INFINITY]
+    @array = ArrowFormat::Float32Array.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [-Float::INFINITY, -0.0, +0.0, +Float::INFINITY]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 5))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-float64-array.rb b/ruby/red-arrow-format/test/test-float64-array.rb
index 22393637cfa9..92099f1cd06d 100644
--- a/ruby/red-arrow-format/test/test-float64-array.rb
+++ b/ruby/red-arrow-format/test/test-float64-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestFloat64Array < Test::Unit::TestCase
+  def setup
+    @values = [-Float::INFINITY, nil, +Float::INFINITY]
+    @array = ArrowFormat::Float64Array.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [-Float::INFINITY, -0.0, +0.0, +Float::INFINITY]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 5))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-int16-array.rb b/ruby/red-arrow-format/test/test-int16-array.rb
index f98650895af6..ddfdcc5ddc53 100644
--- a/ruby/red-arrow-format/test/test-int16-array.rb
+++ b/ruby/red-arrow-format/test/test-int16-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestInt16Array < Test::Unit::TestCase
+  def setup
+    @values = [-(2 ** 15), nil, (2 ** 15) - 1]
+    @array = ArrowFormat::Int16Array.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [-(2 ** 15), (2 ** 15) - 1]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-int32-array.rb b/ruby/red-arrow-format/test/test-int32-array.rb
index 343c2cc61064..9940a323f452 100644
--- a/ruby/red-arrow-format/test/test-int32-array.rb
+++ b/ruby/red-arrow-format/test/test-int32-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestInt32Array < Test::Unit::TestCase
+  def setup
+    @values = [-(2 ** 31), nil, (2 ** 31) - 1]
+    @array = ArrowFormat::Int32Array.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [-(2 ** 31), (2 ** 31) - 1]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-int64-array.rb b/ruby/red-arrow-format/test/test-int64-array.rb
index d265b5da7184..b5db1d163c79 100644
--- a/ruby/red-arrow-format/test/test-int64-array.rb
+++ b/ruby/red-arrow-format/test/test-int64-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestInt64Array < Test::Unit::TestCase
+  def setup
+    @values = [-(2 ** 63), nil, (2 ** 63) - 1]
+    @array = ArrowFormat::Int64Array.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [-(2 ** 63), (2 ** 63) - 1]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-int8-array.rb b/ruby/red-arrow-format/test/test-int8-array.rb
index 8c802a9b7f3d..459674f9fd20 100644
--- a/ruby/red-arrow-format/test/test-int8-array.rb
+++ b/ruby/red-arrow-format/test/test-int8-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestInt8Array < Test::Unit::TestCase
+  def setup
+    @values = [-(2 ** 7), nil, (2 ** 7) - 1]
+    @array = ArrowFormat::Int8Array.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [-(2 ** 7), (2 ** 7) - 1]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-large-binary-array.rb b/ruby/red-arrow-format/test/test-large-binary-array.rb
index 67e55dd1b68b..0fc7a1132808 100644
--- a/ruby/red-arrow-format/test/test-large-binary-array.rb
+++ b/ruby/red-arrow-format/test/test-large-binary-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestLargeBinaryArray < Test::Unit::TestCase
+  def setup
+    @values = ["\x00\x01".b, nil, "\xff\x10".b]
+    @array = ArrowFormat::LargeBinaryArray.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = ["\x00\x01".b, "\xff\x10".b]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-large-utf8-array.rb b/ruby/red-arrow-format/test/test-large-utf8-array.rb
index 1ee4a3994512..084f3b5ff9a0 100644
--- a/ruby/red-arrow-format/test/test-large-utf8-array.rb
+++ b/ruby/red-arrow-format/test/test-large-utf8-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestLargeUTF8Array < Test::Unit::TestCase
+  def setup
+    @values = ["Hello", nil, "World"]
+    @array = ArrowFormat::LargeUTF8Array.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = ["Hello", "World"]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-month-day-nano-interval-array.rb b/ruby/red-arrow-format/test/test-month-day-nano-interval-array.rb
index 1c965c6813c1..26842d930246 100644
--- a/ruby/red-arrow-format/test/test-month-day-nano-interval-array.rb
+++ b/ruby/red-arrow-format/test/test-month-day-nano-interval-array.rb
@@ -16,6 +16,15 @@
 # under the License.
 
 class TestMonthDayNanoIntervalArray < Test::Unit::TestCase
+  def setup
+    @values = [
+      [1, 1, 100],
+      nil,
+      [3, 3, 300],
+    ]
+    @array = ArrowFormat::MonthDayNanoIntervalArray.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [
@@ -90,4 +99,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-null-array.rb b/ruby/red-arrow-format/test/test-null-array.rb
index 961f2cd8d49f..c66de5517ef3 100644
--- a/ruby/red-arrow-format/test/test-null-array.rb
+++ b/ruby/red-arrow-format/test/test-null-array.rb
@@ -16,6 +16,10 @@
 # under the License.
 
 class TestNullArray < Test::Unit::TestCase
+  def setup
+    @array = ArrowFormat::NullArray.new(3)
+  end
+
   def test_initialize
     assert_equal([nil] * 9,
                  ArrowFormat::NullArray.new(9).to_a)
@@ -34,4 +38,8 @@ def test_sliced
       assert_equal(array1, array2.slice(1, 3))
     end
   end
+
+  def test_aref
+    assert_nil(@array[1])
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-time32-array.rb b/ruby/red-arrow-format/test/test-time32-array.rb
index 98e865d9e25c..74a01dc6d75e 100644
--- a/ruby/red-arrow-format/test/test-time32-array.rb
+++ b/ruby/red-arrow-format/test/test-time32-array.rb
@@ -19,6 +19,8 @@ class TestTime32Array < Test::Unit::TestCase
   def setup
     @time_00_00_10 = 10
     @time_00_01_10 = 60 + 10
+    @values = [@time_00_00_10, nil, @time_00_01_10]
+    @array = ArrowFormat::Time32Array.new(:second, @values)
   end
 
   sub_test_case("#initialize") do
@@ -57,4 +59,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-time64-array.rb b/ruby/red-arrow-format/test/test-time64-array.rb
index 3625a1917f27..dd7a08ad2fd3 100644
--- a/ruby/red-arrow-format/test/test-time64-array.rb
+++ b/ruby/red-arrow-format/test/test-time64-array.rb
@@ -19,6 +19,8 @@ class TestTime64Array < Test::Unit::TestCase
   def setup
     @time_00_00_10_000_000 = 10 * 1_000_000
     @time_00_01_10_000_000 = (60 + 10) * 1_000_000
+    @values = [@time_00_00_10_000_000, nil, @time_00_01_10_000_000]
+    @array = ArrowFormat::Time64Array.new(:microsecond, @values)
   end
 
   sub_test_case("#initialize") do
@@ -57,4 +59,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-timestamp-array.rb b/ruby/red-arrow-format/test/test-timestamp-array.rb
index 397a01a64f02..c2f73e366c07 100644
--- a/ruby/red-arrow-format/test/test-timestamp-array.rb
+++ b/ruby/red-arrow-format/test/test-timestamp-array.rb
@@ -19,6 +19,12 @@ class TestTimestampArray < Test::Unit::TestCase
   def setup
     @timestamp_2019_11_17_15_09_11 = 1574003351
     @timestamp_2025_12_16_05_33_58 = 1765863238
+    @values = [
+      @timestamp_2019_11_17_15_09_11,
+      nil,
+      @timestamp_2025_12_16_05_33_58,
+    ]
+    @array = ArrowFormat::TimestampArray.new(:second, @values)
   end
 
   sub_test_case("#initialize") do
@@ -83,4 +89,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-uint16-array.rb b/ruby/red-arrow-format/test/test-uint16-array.rb
index 736cb7494a47..3c5ad6aceab5 100644
--- a/ruby/red-arrow-format/test/test-uint16-array.rb
+++ b/ruby/red-arrow-format/test/test-uint16-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestUInt16Array < Test::Unit::TestCase
+  def setup
+    @values = [0, nil, (2 ** 16) - 1]
+    @array = ArrowFormat::UInt16Array.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [0, (2 ** 16) - 1]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-uint32-array.rb b/ruby/red-arrow-format/test/test-uint32-array.rb
index ab6188d7b6eb..079a96cbf59b 100644
--- a/ruby/red-arrow-format/test/test-uint32-array.rb
+++ b/ruby/red-arrow-format/test/test-uint32-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestUInt32Array < Test::Unit::TestCase
+  def setup
+    @values = [0, nil, (2 ** 32) - 1]
+    @array = ArrowFormat::UInt32Array.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [0, (2 ** 32) - 1]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-uint64-array.rb b/ruby/red-arrow-format/test/test-uint64-array.rb
index 781bc6376d15..c43808273577 100644
--- a/ruby/red-arrow-format/test/test-uint64-array.rb
+++ b/ruby/red-arrow-format/test/test-uint64-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestUInt64Array < Test::Unit::TestCase
+  def setup
+    @values = [0, nil, (2 ** 64) - 1]
+    @array = ArrowFormat::UInt64Array.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [0, (2 ** 64) - 1]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-uint8-array.rb b/ruby/red-arrow-format/test/test-uint8-array.rb
index ae33f910ef21..bd03aa0efbc9 100644
--- a/ruby/red-arrow-format/test/test-uint8-array.rb
+++ b/ruby/red-arrow-format/test/test-uint8-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestUInt8Array < Test::Unit::TestCase
+  def setup
+    @values = [0, nil, (2 ** 8) - 1]
+    @array = ArrowFormat::UInt8Array.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [0, (2 ** 8) - 1]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-utf8-array.rb b/ruby/red-arrow-format/test/test-utf8-array.rb
index 2970d77793e2..eb6e669e2e5a 100644
--- a/ruby/red-arrow-format/test/test-utf8-array.rb
+++ b/ruby/red-arrow-format/test/test-utf8-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestUTF8Array < Test::Unit::TestCase
+  def setup
+    @values = ["Hello", nil, "World"]
+    @array = ArrowFormat::UTF8Array.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = ["Hello", "World"]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end
diff --git a/ruby/red-arrow-format/test/test-year-month-interval-array.rb b/ruby/red-arrow-format/test/test-year-month-interval-array.rb
index 5004dfb9b02c..29bd61a1ef6c 100644
--- a/ruby/red-arrow-format/test/test-year-month-interval-array.rb
+++ b/ruby/red-arrow-format/test/test-year-month-interval-array.rb
@@ -16,6 +16,11 @@
 # under the License.
 
 class TestYearMonthIntervalArray < Test::Unit::TestCase
+  def setup
+    @values = [0, nil, 100]
+    @array = ArrowFormat::YearMonthIntervalArray.new(@values)
+  end
+
   sub_test_case("#initialize") do
     def test_no_null
       values = [0, 100]
@@ -52,4 +57,14 @@ def test_sliced_different_content
       assert_not_equal(array1, array2.slice(1, 3))
     end
   end
+
+  sub_test_case("#[]") do
+    def test_valid
+      assert_equal(@values[3], @array[3])
+    end
+
+    def test_null
+      assert_nil(@array[1])
+    end
+  end
 end