Add Assert About An Object's Attributes With RSpec as a ruby til

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 For a steady stream of TILs from a variety of rocketeers, checkout
 [til.hashrocket.com](https://til.hashrocket.com/).
 
-_813 TILs and counting..._
+_814 TILs and counting..._
 
 ---
 
@@ -608,6 +608,7 @@ _813 TILs and counting..._
 
 - [A Shorthand For Rerunning Failed Tests With RSpec](ruby/a-shorthand-for-rerunning-failed-tests-with-rspec.md)
 - [Are They All True?](ruby/are-they-all-true.md)
+- [Assert About An Object's Attributes With RSpec](ruby/assert-about-an-objects-attributes-with-rspec.md)
 - [Assoc For Hashes](ruby/assoc-for-hashes.md)
 - [Block Comments](ruby/block-comments.md)
 - [Chaining Multiple RSpec Change Matchers](ruby/chaining-multiple-rspec-change-matchers.md)

ruby/assert-about-an-objects-attributes-with-rspec.md

@@ -0,0 +1,31 @@
+# Assert About An Object's Attributes With RSpec
+
+When testing an object that gets created as the result of some process, it can
+be useful to assert about the attributes of that object. Not all of the
+attributes are relevant and some can be hard to reliably test. Rather than
+asserting about the result of calling `#attributes` or `#to_h` on an object, we
+can focus in with the [`have_attributes`
+matcher](https://relishapp.com/rspec/rspec-expectations/docs/built-in-matchers/have-attributes-matcher)
+provided by RSpec.
+
+```ruby
+RSpec.describe "have_attributes" do
+  it "can assert on an ActiveRecord object" do
+    book = Book.create(title: "Fledling", isbn: "123")
+
+    expect(book).to have_attributes(title: "Fledgling", isbn: "123")
+  end
+
+  it "can assert on a Struct" do
+    Name = Struct.new(:first, :last)
+    some_name = Name.new("Liz", "Lemon")
+
+    expect(some_name).to have_attributes(first: "Liz")
+  end
+end
+```
+
+In this example we were able to assert about all or just a subset of the
+attributes on both an `ActiveRecord` object and a `Struct`.
+
+See [the docs](https://relishapp.com/rspec/rspec-expectations/docs/built-in-matchers/have-attributes-matcher) for more details.