before :each blocks can use let values declared later, enabling per-context setup without predeclaring variables; local variables inside it blocks do not work.

Rails specs can get controller, model, or request helpers from directory-based inference; :type forces the desired context even when a file lives elsewhere.

Capybara has_css? can assert selector counts and text content, including substring matches; exact text requires finding the element and comparing it directly.

NaN is difficult to compare in JavaScript because it never equals itself. Object.is() works in ES6; ES5 needs a number type check plus isNaN().

allow_value and other shoulda-matchers methods can disappear under Rails 4.1 with Spring, causing NoMethodError despite the gem being listed.

Adds colorized terminal output to common Linux commands, making logs and status output easier to scan in the shell.

Jasmine spy assertions can match invocation arguments by type, partial object shape, or any value using jasmine.any(), jasmine.objectContaining(), and jasmine.anything().

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

cucumber.yml may be valid while rerun.txt is corrupted by parallel Cucumber workers writing at the same time, preventing Cucumber from starting.

RSpec 1.x can leave stubbed class methods in place between examples, causing order-dependent failures when spec file evaluation changes.

Run one Cucumber feature file directly with script/cucumber, or invoke it through rake when speed is less important.

Jasmine describe() throws AfterAll TypeError: Failed to execute 'appendChild' on 'Node' when an object is passed instead of a string.

Cucumber can fail with little or no visible error output; a backtrace, verbose formatter, or debug mode can expose the underlying cause.

Network failures between a host and a single target can be isolated with ping checks and an automatic mtr report by email.

Cucumber failures can open the current page in a browser automatically, avoiding repeated "Then show me the page" reruns and speeding up debugging.

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

Nested patiently blocks now wait independently in Spreewald, preventing detached DOM failures when with_scope reuses cached elements.

Finds a record by any string or number across columns, making Cucumber step definitions more flexible. The bang variant raises ActiveRecord::NotFound when nothing matches.

Selenium can miss browser events such as change during form input; a Cucumber step can fire jQuery-registered events manually with execute_script.

Association values in Machinist blueprints need blocks so Project.make runs per blueprint instance, not once at parse time when RSpec loads.

Lazy let evaluation keeps RSpec examples shorter when a setup call has many required arguments, and lets stubs change the result before the value is used.

VCR integration with Cucumber 4 breaks when use_scenario_name: true is enabled, causing an undefined feature method error in Cucumber::RunningTestCase::TestCase.

Capybara find can return incorrect matches when called on nodes from all, especially with text filters. Use a full selector on the page to scope the search reliably.