Test a PDF download as an HTTP response, not just as a call to PDFKit. In an RSpec Rails request spec, verify the status, PDF content type, attachment disposition, filename, and response body. Stub PDFKit for fast, repeatable request coverage, then run a separate integration test with the real wkhtmltopdf executable to catch renderer and asset-configuration problems.
What a PDF download test should prove
A successful PDF endpoint has two parts: it generates PDF bytes and delivers them according to the route’s public contract. A response can return status 200 while containing an HTML error page, or contain PDF bytes with headers that make a browser display or handle the file incorrectly.
For a downloadable report, check these behaviors:
- Status: usually
200 OKfor a completed request. - Content type:
application/pdf. - Disposition: includes
attachmentwhen the endpoint is intended to prompt a download. - Filename: the expected filename is present in
Content-Disposition. - Body: contains PDF data rather than an HTML page or empty response. Starting with
%PDF-is a useful minimum signature check.
These assertions test what a client receives. They are more useful than asserting only that a controller called a particular PDFKit method, because the response headers and body are the download contract.
Write a fast RSpec Rails request spec
Request specs exercise the route and Rails response stack. RSpec Rails maps request specs to Rails integration tests and provides Rails-aware matchers such as have_http_status. Its README recommends functional request tests over direct controller testing. See the RSpec Rails documentation.
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The example below assumes a report route named report_path, a persisted report fixture or factory, and an endpoint that returns an attachment named report.pdf. Adjust those application-specific details to match your route and promised filename.
# spec/requests/reports_spec.rb
RSpec.describe "Reports", type: :request do
describe "GET /reports/:id.pdf" do
let(:pdf_bytes) { "%PDF-1.4nfixture pdf bytesn%%EOFn" }
before do
allow(PDFKit).to receive(:new).and_return(
instance_double(PDFKit, to_pdf: pdf_bytes)
)
end
it "returns a downloadable PDF" do
get report_path(report, format: :pdf)
expect(response).to have_http_status(:ok)
expect(response.headers["Content-Type"]).to include("application/pdf")
expect(response.headers["Content-Disposition"]).to match(/attachment/i)
expect(response.headers["Content-Disposition"]).to include("report.pdf")
expect(response.body).to start_with("%PDF-")
expect(response.body).to include("%%EOF")
end
end
endThe PDF string is a small test fixture, not a rendered or standards-complete PDF. The signature and end-marker checks are practical sanity checks; they do not validate PDF structure or visual correctness. Keep assertions tied to the endpoint’s public behavior. If your application promises a different filename, disposition, or status, assert that contract instead.
Use a PDFKit double if the application constructs PDFKit with arguments or calls a different method; preserve the real request and response path while replacing only the external rendering work. For example, if the action calls PDFKit.new(html, options).to_pdf, the stub should tolerate or expect the options your implementation relies on rather than accidentally hiding a regression in those options.
Choose the right delivery path: send_data or send_file
Rails supports both returning generated bytes and sending a file already on disk. Test the delivery mechanism your action actually uses; do not make the request spec depend on a file that production does not create, or vice versa. The Rails Action Controller guide documents send_data and send_file, and distinguishes attachment behavior from inline display.
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When the action uses send_data
send_data is appropriate when the PDF is generated as bytes in the request. Exercise the endpoint and assert the response’s content type, disposition, filename, and body just as in the request-spec example. Rails documents send_data as a way to send generated data to the client.
When the action uses send_file
send_file serves a file already on disk. In the test, create a temporary or fixture PDF, have the action serve that file, and verify that the response contains the expected data and headers. This checks the actual file-delivery path rather than only checking that a file exists. Rails documents send_file for sending a file to the client.
Both methods can deliver an attachment. If the response is intended to display a PDF in the browser instead, test the inline disposition your endpoint promises rather than asserting attachment.
Keep real-renderer coverage separate
A stubbed request spec gives fast feedback on routing, authorization and application logic, response construction, headers, filename, and the bytes handed to Rails. It does not prove that wkhtmltopdf is installed, that PDFKit can launch it, or that the rendered template can load its CSS, images, and JavaScript.
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Add a focused integration example or CI job that does not stub PDFKit. Render a representative template with the configured executable and assert the response contract plus a non-empty body. Keep this path separate from the fast request spec: PDFKit invokes an external process, and executable availability or asset URLs can differ between development and CI. See the PDFKit documentation for its wkhtmltopdf integration and troubleshooting guidance.
A useful division of coverage is:
- Fast request spec on routine changes: stub the renderer and cover response behavior deterministically.
- Real-renderer integration coverage: run with the actual executable to catch setup, rendering, and asset-loading failures.
Do not treat a passing signature check in the stubbed test as proof that the rendered document looks right. If visual output matters, the real-renderer path must exercise a representative template and its resource dependencies.
Configure wkhtmltopdf and assets explicitly
If the test environment cannot find the executable, configure PDFKit with its path. The path must point to an executable available in that environment; a developer-machine path will not automatically exist in CI.
PDFKit.configure do |config|
config.wkhtmltopdf = "/path/to/wkhtmltopdf"
endRelative asset references can also fail when the renderer does not resolve them in the application’s request context. PDFKit documents root_url and protocol options for resolving relative resources. Use absolute asset URLs or configure those options for the renderer environment, then verify the result in the real-renderer test. Missing stylesheets, images, or JavaScript can make a PDF render differently or incompletely even when the HTTP response itself succeeds.
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PDFKit also documents a possible deadlock when wkhtmltopdf calls back into a local application server configured with a single thread. For an integration environment that loads local assets, use multiple server workers or embed resources so the renderer does not need to make callbacks to a blocked server.
Diagnose common failures
| Symptom | Likely cause | What to check or change |
|---|---|---|
| Browser displays text or mishandles the response | The response has the wrong content type. | Inspect Content-Type and return application/pdf. PDFKit specifically calls for that content type for a browser response. |
| Download does not start | The response is inline, or its attachment filename is missing or unexpected. | Inspect Content-Disposition; check for attachment and the promised filename. Rails distinguishes attachment from inline behavior. |
Body begins with HTML instead of %PDF- |
The renderer may have failed, or the endpoint returned an error page. | Use the signature assertion in the fast spec, then inspect the body and renderer output in the real-renderer integration path. |
| CSS or images are missing from the PDF | Relative resources are not resolving in the renderer context. | Use absolute URLs or configure PDFKit’s root_url and protocol options; confirm resource access in the integration environment. |
PDFKit cannot start wkhtmltopdf |
The executable is absent from the environment or not discoverable at the expected path. | Install the executable for that environment and set config.wkhtmltopdf to its actual path. |
| Rendering hangs while loading local assets | The local server may be single-threaded while the renderer calls back into it. | Use multiple workers in the integration environment or embed the resources to avoid callbacks. |
When a failure appears only in CI, first compare the executable path and asset URL configuration between CI and local runs. Keep diagnostics in the real-renderer job; the stubbed request spec should remain independent of machine-specific binaries.
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RSpec Rails compatibility depends on the Rails version. The current RSpec Rails README’s guidance lists 8.x for Rails 8.0 and 7.2, 7.x for Rails 7.x, 6.x for Rails 6.1, 7.0, and 7.1, and 5.x for Rails 5.2 and 6.x. Confirm the matching branch before copying a dependency declaration into an existing application: RSpec Rails version guidance.
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Frequently Asked Questions
Does a PDF signature check prove the file is valid?
No. Checking for %PDF- catches obvious non-PDF responses but does not validate the document’s full structure or visual appearance.
Should the real-renderer integration test run for every request-spec example?
No. Keep routine request coverage fast with PDFKit stubbed, and run focused real-renderer coverage where the executable and asset integration are available.
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