Add support for render_previews in RSpec tests

docs/CHANGELOG.md

@@ -9,6 +9,10 @@ title: Changelog
 
 ## main
 
+* Add support for `render_preview` in RSpec tests.
+
+    *Thomas Hutterer*
+
 * Switch to `standardrb`.
 
     *Joel Hawksley*

lib/view_component/render_preview_helper.rb

@@ -11,15 +11,25 @@ module RenderPreviewHelper
     # ```
     #
     # Note: `#rendered_preview` expects a preview to be defined with the same class
-    # name as the calling test, but with `Test` replaced with `Preview`:
+    # name as the calling test, but with "Test" replaced with "Preview":
     #
     # MyComponentTest -> MyComponentPreview etc.
     #
+    # With RSpec it uses `described_class` plus "Preview" as the class name.
+    #
     # @param preview [String] The name of the preview to be rendered.
     # @return [Nokogiri::HTML]
     def render_preview(name)
       begin
-        preview_klass = self.class.name.gsub("Test", "Preview")
+        preview_klass = if respond_to?(:described_class)
+          if described_class.nil?
+            raise "`render_preview` expected a described_class, but it is nil."
+          end
+
+          "#{described_class}Preview"
+        else
+          self.class.name.gsub("Test", "Preview")
+        end
         preview_klass = preview_klass.constantize
       rescue NameError
         raise NameError.new(

test/sandbox/spec/components/previews/preview_component_spec.rb

@@ -0,0 +1,25 @@
+describe PreviewComponent do
+  include ViewComponent::RenderPreviewHelper
+
+  before do
+    ViewComponent::Preview.load_previews
+  end
+
+  it "renders the preview" do
+    render_preview(:default)
+
+    expect(page).to have_css "h1", text: "Lorem Ipsum"
+  end
+end
+
+describe "PreviewComponent" do
+  include ViewComponent::RenderPreviewHelper
+
+  before do
+    ViewComponent::Preview.load_previews
+  end
+
+  it "raises an error" do
+    expect { render_preview(:default) }.to raise_error(/expected a described_class/)
+  end
+end