Skip to content

05_debugging.md

Latest commit

 

History

History
87 lines (60 loc) · 3.66 KB

05_debugging.md

File metadata and controls

87 lines (60 loc) · 3.66 KB

Debugging Web Applications

This is a Makers Vine. Vines are designed to gradually build up sophisticated skills. They contain a mixture of text and video, and may contain some challenge exercises without proposed solutions. Read more about how to use Makers Vines.

Learn to use Discovery debugging for a web application.

Unit or Integration tests

Remember that unit tests are testing the behaviour of a single class or method in isolation of the rest. This means that unit tests are not concerned with HTTP requests and responses.

Integration tests, on the other end, are testing the full behaviour, from the request to the response, by acting as a web client.

  • If a unit test is failing, fix this first. It means the behaviour of a class or method is broken, regardless of the web application flow.
  • Then, if an integration test is failing, it probably means there is a bug somewhere else in the rest of the application — in the Sinatra route or the HTML view. Following the flow of the data from the client to and from the web server, by also running the server, will help to find out what's wrong.

Getting Visibility

We can get visibility using different tools depending on the "layer":

  • In Sinatra routes or Ruby classes, we can use p to inspect the value of variables or log arbitrary messages. These will be displayed in the terminal, in the logs of the rackup command, which we use to run the web server.
  • In ERB / HTML views, we can use ERB tags to display the value of instance variables set inside the route block (e.g <%= @something %>) so it is displayed as part of the HTML page.
  • We can get visibility into the HTTP request and response — what data is flowing between the client (the web browser) and the server. We can use a client like Postman, or the Browser Developer tools.
  • We can also manually inspect the web page to see what is wrong, or check if Sinatra returns a helpful error message for us.

Exercise

Debug the following web application.

Do the setup and run the server and tests:

cd web-applications/projects_to_debug/postcode_checker_app

bundle install

# Some tests are failing, you'll need to make them pass.
rspec

# In another terminal, to run the server.
rackup

Challenge

Debug the following web application.

Do the setup and run the server and tests:

cd web-applications/projects_to_debug/blog_app

bundle install

# Some tests are failing, you'll need to make them pass.
rspec

# In another terminal, to run the server.
rackup

Next Challenge

How was this resource?
😫 😕 😐 🙂 😀
Click an emoji to tell us.