Add Test For A Subset Of Attributes On A Model as a Rails 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).
 
-_1273 TILs and counting..._
+_1274 TILs and counting..._
 
 ---
 
@@ -852,6 +852,7 @@ _1273 TILs and counting..._
 - [Skip Validations When Creating A Record](rails/skip-validations-when-creating-a-record.md)
 - [Specify New Attributes For #find_or_create_by](rails/specify-new-attributes-for-find-or-create-by.md)
 - [Temporarily Disable strong_params](rails/temporarily-disable-strong-params.md)
+- [Test For A Subset Of Attributes On A Model](rails/test-for-a-subset-of-attributes-on-a-model.md)
 - [Test If An Instance Variable Was Assigned](rails/test-if-an-instance-variable-was-assigned.md)
 - [Test If deliver_later Is Called For A Mailer](rails/test-if-deliver-later-is-called-for-a-mailer.md)
 - [Test Out URL And Path Helpers In The Console](rails/test-out-url-and-path-helpers-in-the-console.md)

rails/test-for-a-subset-of-attributes-on-a-model.md

@@ -0,0 +1,38 @@
+# Test For A Subset Of Attributes On A Model
+
+Let's say you are using RSpec to test some code that creates or updates an
+ActiveRecord object. To evaluate that the code is working, you want to check
+the value of a couple different attributes. Though you could have a series of
+assert statements to check each value, you may want to combine them into a
+single statement.
+
+```ruby
+book = process_that_updates_book(params)
+
+expect(book.attributes).to match(
+  "title" => 'Updated title',
+  "publication_year" => 2001,
+  # ... you have to check *every* attribute
+)
+```
+
+The `#match` matcher requires that every attribute in the hash matches. We
+don't really care to check the `created_at`, `updated_at`, and other irrelevant
+attributes.
+
+Instead, we can `match` on
+[`hash_including`](https://rubydoc.info/gems/rspec-mocks/RSpec%2FMocks%2FArgumentMatchers:hash_including).
+Additionally, we can `symbolize_keys` on the `attributes` to make the expected
+data a little cleaner.
+
+```ruby
+book = process_that_updates_book(params)
+
+expect(book.attributes).to match(hash_including(
+  title: 'Updated title',
+  publication_year: 2001,
+))
+```
+
+If the specified attributes match, then the expectation will pass. If at least
+one of them doesn't, then it will fail. All other attributes are ignored.