Haml can render multi-line Ruby code with the :ruby filter when puts sends generated output into the template response.

RSpec 3 deprecates :should expectations, causing warnings in older test suites and gems that need backward compatibility. RSpec.configure can re-enable both syntax styles.

Custom empty? on a has_many model can break Machinist collection building, creating records with the wrong foreign key. Use explicit association assignment instead.

MySQL 5.6 changed DECIMAL storage and removed the old extra-digit behavior, so columns that relied on it may now need higher precision.

Inline images can leave a small gap below them because they align to the text baseline, reserving space for descenders. vertical-align: middle or display: block removes the gap.

Unexpected GET /__identify__ requests in Capybara test logs come from server readiness checks for Selenium-style drivers; Capybara answers them with middleware when no route exists.

PostgreSQL OVERLAPS treats date ranges as start <= time < end, so boundary dates are excluded and adjacent ranges do not match.

Nested form elements can vanish or submit the wrong data because browsers handle invalid form markup inconsistently, especially during Ajax updates.

FactoryBot transient attributes can pass custom values into associated records, letting parent factories build children with dynamic names and flags.

Capybara.javascript_test? checks whether the current driver supports JavaScript, helping feature tests switch behavior for Selenium, capybara-webkit, Poltergeist, and custom drivers.

BigDecimal#floor returns different types in Ruby 1.8 and 1.9 because it depends on Float#floor; a backport restores the Ruby 1.9 behavior on Ruby 1.8.

bin/webpack-dev-server can fail with Yarn's "Command "webpack-dev-server" not found" error when dependencies are missing; yarn install --check-files restores the command.

Malformed commit timestamps can make git clone fail with badTimezone when strict object validation is enabled. Disabling fetch.fsckobjects works around the error.

Judging legacy code by today’s needs hides the uncertainty faced during initial development, where many architecture and technology choices were made with incomplete information.

Unexpected executable bits can appear on normal project files after copying from Windows or a Samba share. geordi remove-executable-flags clears them recursively with chmod -x.

Records loaded with SQL fragments in :select or :joins become read-only in ActiveRecord to avoid saving rows with noncolumn attributes. :readonly => false overrides the safeguard.

Exchange can discard the plaintext part of multipart/alternative email, leaving only HTML in normal mail accounts and complicating debugging.

Update every entry in a Ruby Hash with a concise merge! trick when each key needs a new computed value.

Limit Unicorn to one worker in development to keep debugging output manageable and prevent concurrent requests like ActionCable from flooding the console.

Connecting Ruby on Ubuntu to Microsoft SQL Server can require nonstandard drivers and native libraries, especially for older SQL Server versions on Linux.

better_errors adds enhanced development error pages with a live REPL, and /__better_errors lets you inspect exceptions from AJAX requests.

any_instance stubbing and expectations now work in RSpec 2.6, enabling should_receive and stub on instances created inside code.