Select2 can be styled to match Bootstrap 4, using a Bootstrap 4 theme fork and matching Sass imports for consistent dropdown controls.

Capistrano rollback hooks let custom deployment tasks undo side effects after a failed release, including Slack notifications and other deployment-specific actions.

Compile Webpacker assets once in parallel test runs and skip recompilation when files are unchanged, avoiding duplicate work and Capybara timeouts.

Detects whether a visible page element is covered by another layer, such as a modal overlay or higher z-index element, using a browser hit test.

CarrierWave can temporarily keep three copies of an uploaded file, and large uploads may waste time and disk space. Configuring moves instead of copies reduces the duplication.

Struct.new can define lightweight Ruby classes with attributes, comparison, and keyword initialization for data objects that behave more like records than hashes.

Rails caching can be enabled for a single RSpec example without changing global test settings. File and memory stores let cache behavior be verified in isolated tests, including parallel runs.

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/.