User-supplied filenames can escape a target directory and expose arbitrary readable files. A guarded send_file helper keeps downloads inside the intended path.

Local HTTPS development often needs a trusted certificate for browser access. Self-signed or CA-signed certificates let localhost or wildcard hostnames run without warning dialogs.

Unique scratch directories prevent flaky tests and stale files in parallel Ruby test runs. Dir.mktmpdir creates them safely and can use a custom base path.

Flaky test suites can fail more often with too many parallel workers; limiting PARALLEL_TEST_PROCESSORS can reduce race-condition failures with only a small runtime cost.

Bundler variables leak into child processes and can force the wrong gemset when running nested bundle commands. Bundler.with_original_env restores the pre-Bundler environment; Bundler.with_unbundled_env is the modern Bundler-free variant.

Avoid duplicated Cucumber scenarios by sharing setup and assertions with step composition, helper modules, or scenario outlines. Better reuse keeps integration tests DRY and stack traces readable.

Geordi 10.0.0 adds console and test-runner fixes, IRB configuration, and safer PostgreSQL dump restoration, with breaking changes to database drop handling.

mysql2 runtime failures can stem from MariaDB/MySQL client library version mismatches on Linux, especially Ubuntu 22.04; LTS branches remove the client-version check.

Integrating makandra-rubocop into an existing Ruby codebase often means handling many current offenses, then fixing cops incrementally without blocking development.

Custom Bundler groups can still be downloaded during Capistrano deploys, slowing production and staging releases. Exclude unnecessary groups with bundle_without to avoid installing unused gems.

View specs can stay fast and readable by querying rendered HTML with Capybara finders and matchers instead of relying on heavier request or feature specs.

Local development can use Passenger Standalone as a zero-configuration Ruby app server with SSL and production-like behavior, replacing Webrick or Thin.

PostgreSQL compares strings case-sensitively, which can break email and username lookups and uniqueness checks. Lowercasing values or using case-insensitive matching avoids common bugs.

Ruby 2.3+ supports <<~ for automatic HEREDOC unindentation; older versions can use ActiveSupport's String#strip_heredoc to remove common leading whitespace.

PostgreSQL DISTINCT ON keeps one ordered row per group, useful for latest-per-user queries and other group-wise maximum results when plain DISTINCT is not enough.

Send HTTP requests from the command line with curl, including custom methods, form data, and basic authentication.

Rack::SteadyETag makes HTML caching effective by keeping ETags stable when only CSRF tokens or CSP nonces change.

Haml indentation can leak into preformatted text and textareas, adding unwanted leading spaces. Using ~ instead of = preserves whitespace without extra indentation.

SimpleForm's :grouped_select can be awkward when you already have a flat collection and need grouped options. A group_by extension makes optgroup labels easier to derive.

Migrating CoffeeScript from Sprockets to Webpacker can keep existing classes and dependencies working by adding coffee-loader and adjusting imports and global namespace exposure.

attribute? often checks presence like attribute.present?, but numeric values and associations behave differently; 0 can be false for ActiveRecord query attributes.