Add Configure Tests To Run In Random Order as an RSpec TIL

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1437 TILs and counting..._
+_1438 TILs and counting..._
 
 ---
 
@@ -1101,6 +1101,7 @@ _1437 TILs and counting..._
 
 - [Avoid Accidentally Disabling Pry](rspec/avoid-accidentally-disabling-pry.md)
 - [Check Specific Arguments To Received Method](rspec/check-specific-arguments-to-received-method.md)
+- [Configure Tests To Run In Random Order](rspec/configure-tests-to-run-in-random-order.md)
 - [Find Minimal Set Of Tests Causing A Flicker](rspec/find-minimal-set-of-tests-causing-a-flicker.md)
 - [Format Test Results As A JSON File](rspec/format-test-results-as-a-json-file.md)
 - [Run Tests With Documentation Formatting](rspec/run-tests-with-documentation-formatting.md)

rspec/configure-tests-to-run-in-random-order.md

@@ -0,0 +1,33 @@
+# Configure Tests To Run In Random Order
+
+By default, an RSpec test suite is going to run in a predictable, sequential
+order, every time.
+
+When testing the parts of a complex Rails app that have all kinds of test data
+that needs to be set up, I prefer to have my tests always run in a random
+(repeatable with a seed) order. This way I'm more likely to catch sooner,
+rather than later, bugs that are hidden by passing tests due to test data setup
+that happens to work in a specific order.
+
+RSpec can be configured to run tests in a random, seedable order in the
+`spec_helper.rb` file.
+
+```ruby
+RSpec.configure do |config|
+  config.order = :random
+end
+```
+
+Whenever you run your test suite, the first thing you'll see is a message like
+this:
+
+```
+Randomized with seed 7011
+```
+
+That seed number can be used to re-run the suite in a repeatable order when you
+need to do so to track down an order-dependent failing test.
+
+```bash
+$ be rspec --seed 7011
+```