how_to_reach

The problem

Testing with real collaborators costs more setup than testing with doubles. To call Invoice#total on a real object you need an Invoice with line items, and the items need a sku the price table knows. The source does not list which of those are required or the order to build them in, so you read the code, guess, and debug the guess.

The cost of that setup is a reason people use doubles when they would prefer real objects.

The fix

Your agent can ask while it writes an integration spec:

$ ra how_to_reach Invoice#total

Invoice#total
· seen_in: spec/models/invoice_spec.rb:6
- LineItem.new(sku: String)
- Invoice#add_line(item: LineItem, quantity: Integer)
- Invoice#total
Objects built outside traced code (factories, fixtures, seeds) appear only as the class of an argument.

The agent turns that list into setup that uses real objects throughout. The path was recorded from spec/models/invoice_spec.rb:6, which contains that setup:

invoice = Invoice.new(account: account, number: "INV-1", issued_on: Date.current)
invoice.add_line(item: LineItem.new(sku: "A1"), quantity: 2)

expect(invoice.total).to eq(Money.new(2_880, "GBP"))

The classes and the call order come from the recording, and you supply the values. ra scaffold Invoice#total goes one step further and drafts the example.

How it works

The recording keeps object identity. how_to_reach finds a recorded call to the target method, takes its receiver and arguments, and walks backwards through the same call tree to the traced calls that built or returned those objects, in order. Of all the recorded ways to reach the method it prefers one that built real objects over one that was passed doubles, then the shortest, and it names the spec example the path came from.

Run it on your app

The output on this page comes from our example Rails app, and it is regenerated whenever a tool changes. These are the commands behind it. On your own app, run ra record first, then put your own class, method or file in their place.

ra how_to_reach 'Invoice#total'
ra scaffold 'Invoice#total'

The recorded setup is spec/models/invoice_spec.rb:6, and the method is app/models/invoice.rb:35.

Reading the result

• A construction step appears when the constructor is traced. Invoice.new is ActiveRecord’s constructor and a factory’s create runs in gem code, so the invoice itself is not a step in the path. LineItem.new is defined in the app, so it appears.
• --avoid Klass skips paths that go through a class you would prefer not to depend on.

Every tool reads the same recording. What gets recorded and how far to trust an answer are on the questions page.

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