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Pry-ing into a Stack Trace

I was recently working on a feature, committed what I thought was clean code, and started getting errors. I git stashed, and re-ran my tests, and still got errors. Here’s the full stacktrace:

> b ruby -Itest test/models/model_name_redacted_test.rb -n=/errors/

# Running tests with run options -n=/errors/ --seed 55842:

/Users/joshthompson/.rvm/gems/ruby-2.3.7/gems/minitest-reporters-1.3.5/lib/minitest/reporters/default_reporter.rb:49:in `after_suite': undefined method `name' for nil:NilClass (NoMethodError)
	from /Users/joshthompson/.rvm/gems/ruby-2.3.7/gems/minitest-reporters-1.3.5/lib/minitest/reporters/base_reporter.rb:59:in `report'
	from /Users/joshthompson/.rvm/gems/ruby-2.3.7/gems/minitest-reporters-1.3.5/lib/minitest/reporters/default_reporter.rb:89:in `report'
	from /Users/joshthompson/.rvm/gems/ruby-2.3.7/gems/minitest-reporters-1.3.5/lib/minitest/minitest_reporter_plugin.rb:26:in `each'
	from /Users/joshthompson/.rvm/gems/ruby-2.3.7/gems/minitest-reporters-1.3.5/lib/minitest/minitest_reporter_plugin.rb:26:in `report'
	from /Users/joshthompson/.rvm/gems/ruby-2.3.7/gems/minitest-5.11.3/lib/minitest.rb:808:in `each'
	from /Users/joshthompson/.rvm/gems/ruby-2.3.7/gems/minitest-5.11.3/lib/minitest.rb:808:in `report'
	from /Users/joshthompson/.rvm/gems/ruby-2.3.7/gems/minitest-5.11.3/lib/minitest.rb:141:in `run'
	from /Users/joshthompson/.rvm/gems/ruby-2.3.7/gems/minitest-5.11.3/lib/minitest.rb:63:in `block in autorun'
Coverage report generated for Unit Tests to /Users/joshthompson/wombat/threatsim-rails/threatsim/coverage. 1512 / 17964 LOC (8.42%) covered.

This is a relatively common error. Something is nil where it ought not to be nil.

But now for the kicker.

I found out that if you hold the cmd key down and click one of those file paths, the file in question will open in your editor!!!

AND YOU CAN JUST PUT A PRY IN THERE SOMEWHERE AND YOU’LL HIT IT NEXT TIME THAT LINE OF CODE EXECUTES!!!

AAAAAHHHHH HOW DID I NOT KNOW THIS??? I’ve been writing code full-time for two years, and did not know I could do this!

OK, I am breathing fine. Shall we unpack this?

Lets run the test. It’ll cause an error, with a stack trace. Hold down the cmd key, and mouse over the path, as you would a URL:

cmd and mouseover

Great. Now click it.

The file you selected gets opened up in your current text editor, with the cursor at the line in question!

In this case, it’s minitest/reporters/default_reporter.rb:49, which is a gem bound to a specific ruby version, managed by RVM, so the path also includes .rvm/gems/ruby-2.3.7/gems/, which is in /Users/joshthompson/, so the full path is:

/Users/joshthompson/.rvm/gems/ruby-2.3.7/gems/minitest-reporters-1.3.5/lib/minitest/reporters/default_reporter.rb:49

file opens

You can stick a pry in there to pause execution and poke around.

pry ready to go

Run the test again, and execution pauses at the pry. (In this case, the super keyword bumps where the pry hits to the superclass.)

exploring the context

The long story short is - I was passing a name flag to Minitest, and it couldn’t find a test by that name.

I wouldn’t have figured this out except for exploring the source code - I would have kept rolling back my commits, thinking that I’d botched my code somewhere.

Being able to quickly explore the source code of Ruby gems and interact with those gems in a pry sessions is a complete game changer.

Here’s what the all_reporters object looked like, by the way:

all reporters

This is huge. I’m so excited about this.

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