Selecting XML namespace elements with CSS in Nokogiri requires | instead of : for namespaced names like soapenv|Envelope.

Cucumber can report cucumber.yml as invalid even when it parses correctly; an invalid rerun file like tmp/rerun.txt may trigger the error.

RSpec tests are easier to maintain with clearer structure and disciplined style, but recommendations still need judgment; the Self-Contained Test is a complementary approach.

Mock expectations in RSpec can linger across examples; resetting a proxy removes the configured doubles and returns the object to its original state.

Conditional cron jobs in whenever can target only one Rails environment or Capistrano stage, avoiding unwanted tasks on other deployments.

Ruby method dispatch follows a fixed lookup chain across singleton classes, prepended modules, class methods, included modules, and superclasses.

Rake tasks can be verified in RSpec by expecting Rake::Task to receive invoke, useful for testing task-triggered side effects without putting logic in tasks.

git commit --fixup creates a follow-up commit that git rebase --autosquash can fold into an earlier change, keeping feature-branch history tidy.

Run several MySQL releases side by side in one Linux account for testing or Rails development, using isolated sandboxes on separate ports.

Scopes defined as class methods can drop earlier filters when they return self; use all to preserve chained conditions in Rails 2 and 5.

Rubygems 3.1+ adds a Gem::Specification#rubyforge_project deprecation warning that can clutter development logs; installing 3.0.8 avoids it on older projects.

Stage only matching lines from a large git diff and commit them separately by filtering hunks with grepdiff before git apply --cached.

A curated set of 900+ personal programming tips spans Ruby, Rails, Git, Unix, Chrome, and JavaScript, with many small shortcuts for daily development work.

Puma concurrency in Rails depends on workers and threads; self-calls during a request can deadlock in development or tests unless multiple workers are enabled.

Code coverage reveals untested Rails paths and blind spots across RSpec, Cucumber, and parallel test runs. SimpleCov can separate reports and add branch coverage.

#dup and #clone only copy the top level of nested hashes and arrays; #deep_dup duplicates the full structure, but cycles can trigger SystemStackError.

Limit Chrome CPU speed to measure frontend performance and reproduce sluggish behavior in DevTools.

Browser video playback depends on container and codec support; MP4 with H.264 and AAC works broadly, while WebM can serve modern clients and downloads need native playback support.

Force Devise to use browser Basic Auth instead of the HTML sign-in form by enabling http_authenticatable and removing navigational formats.

Comments work best when they explain why code exists, not what it does, and stay close to the relevant code, robust against change.