Conditional Rails validations with if: are not covered by Shoulda Matchers; test the model’s behavior by stubbing the predicate and checking presence only when it applies.

Serve raw GitHub files with correct Content-Type headers for CDN-style testing or prototyping, but without any uptime guarantee.

ONLY_FULL_GROUP_BY in MySQL 5.7 rejects queries that select non-grouped columns, preventing nondeterministic results and breaking some Rails scopes.

Manipulating PostgreSQL array columns can be awkward: values can be appended, removed, or replaced, with special handling for multi-value substitutions.

ChromeDriver click targeting can hit the wrong point on an element, causing intercepted or non-clickable errors when overlays or nearby elements overlap.

Rails 5 model classes inherit from ApplicationRecord, making it the shared home for logic used by all application models instead of patching ActiveRecord::Base.

Deploy a single server from a multi-server Capistrano setup by using HOSTFILTER to target one host and skip irrelevant tasks.

Ubuntu keyring passwords can differ from the current user password after later password changes. If the old password is unknown, the affected keyring may need to be deleted in Passwords and Keys (seahorse).

Global website checks reveal DNS propagation issues and location-specific rendering problems before users do.

Percentage padding-top can create a responsive box whose height follows its width, useful for keeping background images proportional without fixed heights.

hash_including in WebMock v3.0.1 compares query values as strings, so integer expectations fail unless the request matcher uses '1' instead of 1.

gem list -r --clear-sources -s can inspect gems on a private remote server, useful when Bundler reports a gem in multiple sources.

Ruby's standard library is being gemified, so components can be updated independently of Ruby and API breaks can be fixed before a full Ruby upgrade.

Browser HTTP/2 push support is inconsistent and can hurt performance instead of improving it, despite a useful model for integrating push with browser APIs.

RSpec stubs for methods that yield blocks need and_yield instead of and_return; multiple yields can be chained, and return values can be combined.

Middleman pretty URLs can trigger an extra redirect and second page request; Apache can serve /foo/index.html directly while canonicalizing /foo/.

Rails-friendly Middleman setup for live reload, asset pipeline, i18n, environment-specific config, browser testing, and Capistrano deployment.

Firewall or proxy settings can block Capistrano from reaching a Git repository and stop deployments. Using an HTTP proxy or an SSH tunnel restores repository access.

Print Ruby objects in aligned columns in the console for quick record comparison and attribute inspection.

Restore a deleted or removed file in Git and undo a staged deletion without committing, using the index and git checkout -- correctly.

LoadError occurs when a Ruby gem is required outside Gemfile or .gemspec; adding its install path to $: allows temporary loading for debugging.

Resolve Git merge conflicts locally in RubyMine with a visual three-pane tool for comparing versions and choosing changes.

Use an iPhone’s cellular data connection on Ubuntu over USB by installing iPhone tethering packages and enabling Personal Hotspot.