Cover more with tests

test/active_model_serializers/transform_test.rb

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+require 'test_helper'
+
+class ActiveModelSerializers::TransformTest < ActiveSupport::TestCase
+  def test_camel
+    obj = Object.new
+    scenarios = [
+      {
+        value: { :some_key => 'value' },
+        expected: { :SomeKey => 'value' }
+      },
+      {
+        value: { 'some_key' => 'value' },
+        expected: { 'SomeKey' => 'value' }
+      },
+      {
+        value: :some_value,
+        expected: :SomeValue
+      },
+      {
+        value: obj,
+        expected: obj
+      },
+      {
+        value: nil,
+        expected: nil
+      }
+    ]
+    scenarios.each do |s|
+      result = ActiveModelSerializers::Transform.camel(s[:value])
+      assert_equal s[:expected], result
+    end
+  end
+
+  def test_camel_lower
+    obj = Object.new
+    scenarios = [
+      {
+        value: { :some_key => 'value' },
+        expected: { :someKey => 'value' }
+      },
+      {
+        value: { 'some_key' => 'value' },
+        expected: { 'someKey' => 'value' }
+      },
+      {
+        value: :some_value,
+        expected: :someValue
+      },
+      {
+        value: obj,
+        expected: obj
+      },
+      {
+        value: nil,
+        expected: nil
+      }
+    ]
+    scenarios.each do |s|
+      result = ActiveModelSerializers::Transform.camel_lower(s[:value])
+      assert_equal s[:expected], result
+    end
+  end
+
+  def test_dash
+    obj = Object.new
+    scenarios = [
+      {
+        value: { :some_key => 'value' },
+        expected: { :"some-key" => 'value' }
+      },
+      {
+        value: { 'some_key' => 'value' },
+        expected: { 'some-key' => 'value' }
+      },
+      {
+        value: :some_value,
+        expected: :"some-value"
+      },
+      {
+        value: obj,
+        expected: obj
+      },
+      {
+        value: nil,
+        expected: nil
+      }
+    ]
+    scenarios.each do |s|
+      result = ActiveModelSerializers::Transform.dash(s[:value])
+      assert_equal s[:expected], result
+    end
+  end
+
+  def test_underscore
+    obj = Object.new
+    scenarios = [
+      {
+        value: { :"some-key" => 'value' },
+        expected: { :some_key => 'value' }
+      },
+      {
+        value: { 'some-key' => 'value' },
+        expected: { 'some_key' => 'value' }
+      },
+      {
+        value: :"some-value",
+        expected: :some_value
+      },
+      {
+        value: obj,
+        expected: obj
+      },
+      {
+        value: nil,
+        expected: nil
+      }
+    ]
+    scenarios.each do |s|
+      result = ActiveModelSerializers::Transform.underscore(s[:value])
+      assert_equal s[:expected], result
+    end
+  end
+end