Add Find Minimal Set Of Tests Causing A Flicker as an RSpec TIL

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).
 
-_1162 TILs and counting..._
+_1163 TILs and counting..._
 
 ---
 
@@ -876,6 +876,7 @@ _1162 TILs and counting..._
 ### RSpec
 
 - [Check Specific Arguments To Received Method](rspec/check-specific-arguments-to-received-method.md)
+- [Find Minimal Set Of Tests Causing A Flicker](rspec/find-minimal-set-of-tests-causing-a-flicker.md)
 
 ### Ruby
 

rspec/find-minimal-set-of-tests-causing-a-flicker.md

@@ -0,0 +1,27 @@
+# Find Minimal Set Of Tests Causing Flicker
+
+You have a pretty reliable test suite. However, every once in a while CI will
+fail. It fails for some test that doesn't seem to be related to the PR. And if
+you re-run CI, it may not fail a subsequent time.
+
+Your test suite has a flicker.
+
+Because this flickering test fails so sporadically, it can be hard to track
+down when it fails and why.
+
+[RSpec comes with a `--bisect`
+flag](https://relishapp.com/rspec/rspec-core/docs/command-line/bisect) that can
+help you track down the _minimal_ sequence of tests that will produce a
+failure. So, the next time CI fails unexpectedly on this flickering test, grab
+the seed for that test run and use it locally to perform a bisect.
+
+```bash
+$ rspec --seed 1234 --bisect
+```
+
+This while take a while to run, but when it is done, it should output an
+`rspec` command with a series of specific tests. Copy, paste, and run this
+command as you work on tracking down the issue. One strong possibility is that
+one test is altering some global state in a way that the other test doesn't
+expect. And it is only in this order that you can see that manifest as a
+failure.