Allow Rails::Form root namespace to be given a custom key

This adds flexibility in how your (customized) form can be reused
with different models.

[#52]

Author: Marco van Kampen

lib/superform/rails.rb

@@ -74,12 +74,12 @@ def title
         end
       end
 
-      def initialize(model, action: nil, method: nil, **attributes)
+      def initialize(model, action: nil, method: nil, namespace: nil, **attributes)
         @model = model
         @action = action
         @method = method
         @attributes = attributes
-        @namespace = Namespace.root(key, object: model, field_class: self.class::Field)
+        @namespace = Namespace.root(namespace || key, object: model, field_class: self.class::Field)
       end
 
       def around_template(&)

spec/superform/rails/form_spec.rb

@@ -0,0 +1,17 @@
+RSpec.describe Superform::Rails::Form do
+  let(:model) { double('MockModel', model_name: double(param_key: 'mock_model')) }
+
+  it 'creates a root namespace based on the active model' do
+    expect(Superform::Namespace).to receive(:root).with('mock_model', any_args)
+
+    described_class.new(model)
+  end
+
+  context 'override root namespace with an argument' do
+    it 'creates a root namespace based on the active model' do
+      expect(Superform::Namespace).to receive(:root).with('user', any_args)
+
+      described_class.new(model, namespace: 'user')
+    end
+  end
+end