Rails 3 can issue internal HTTP requests through the Rack interface, useful for Cucumber features and testing app responses without a browser.

Responsive breakpoints can be checked in JavaScript with matchMedia() instead of duplicating CSS logic, and MediaQueryList change events track width updates efficiently.

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

Unused database columns confuse teams and can linger safely while legacy access is phased out. ignored_columns removes Rails accessors and helps flag fields for later removal.

Delegated jQuery events can be hard to fire programmatically for testing; native dispatchEvent with the right event class works better than trigger in many cases.

Zero-downtime migration from Elasticsearch to OpenSearch for Searchkick apps, including staging validation, client switching, and environment-specific index settings.

Rails file storage migration with background jobs, reruns, and URL rewrites; large media backfills need careful testing, queue tuning, and fallback handling.

Rails API backends can be fast and easy to extend, but serializer maintenance, schema drift, documentation limits, and missing rate limits create real operational risks.

Array comparisons in Jasmine need different matchers for exact order, unordered equality, or subset checks when testing collections.

Transparent apple-touch-icon images on iOS turn black in Safari, so solid backgrounds prevent ugly home-screen and bookmark icons.

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

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.

Custom RSpec matcher for checking allowed association values, useful when validating assignable_values on model associations.

Readable Jasmine specs can use async/await for promises, async setup, event waiting, and controllable async spies instead of done callbacks.

Single-line text can overflow its container in Rails views; text-overflow: ellipsis and white-space: nowrap produce cleaner truncation in supported browsers.

Dynamically created symbols can make keyword arguments turn nil in Ruby 2.2 when a method uses several keywords and **options.

A library for testing a Ruby gem against multiple Ruby, dependency and database combinations, with shared local and CI setup for full permutation coverage.

hash_including cannot match nested hashes reliably; use nested matchers such as include or another hash_including for partial hash checks.

ActiveRecord :include can switch between separate queries and SQL joins, causing ambiguous ORDER BY clauses and hidden production bugs when associations are preloaded.

Local Keycloak can emulate a SAML identity provider for development, letting SSO flows and attribute mapping be tested without waiting on an external IDP.