Add Assert Two Arrays Have The Same Items With RSpec as a rails til

Author: jbranchaud

README.md

@@ -9,7 +9,7 @@ and pairing with smart people at Hashrocket.
 
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-_884 TILs and counting..._
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@@ -509,6 +509,7 @@ _884 TILs and counting..._
 - [ActiveRecord Query For This Or That](rails/active-record-query-for-this-or-that.md)
 - [Advance The Date](rails/advance-the-date.md)
 - [All or Nothing Database Transactions](rails/all-or-nothing-database-transactions.md)
+- [Assert Two Arrays Have The Same Items With RSpec](rails/assert-two-arrays-have-the-same-items-with-rspec.md)
 - [Attach A File With Capybara](rails/attach-a-file-with-capybara.md)
 - [Attribute Getter without the Recursion](rails/attribute-getter-without-the-recursion.md)
 - [Attribute Was](rails/attribute-was.md)

rails/assert-two-arrays-have-the-same-items-with-rspec.md

@@ -0,0 +1,25 @@
+# Assert Two Arrays Have The Same Items With RSpec
+
+Methods that return arrays of values with inconsistent orderings can be
+annoying to test with the `#eq` matcher. To keep your test from fickering,
+you'd have to ensure the comparison is the same every time.
+
+```ruby
+it "has the correct values" do
+  expect(fetch_colors(params).sort).to eq(["blue", "green", "yellow"])
+end
+```
+
+It'd be better if we could keep our test focused and simple. If sort order
+isn't something we care about, then it shouldn't be part of our test. RSpec has
+a matcher for this kind of scenario --
+[`#match_array`](https://www.rubydoc.info/github/rspec/rspec-expectations/RSpec%2FMatchers:match_array).
+
+```ruby
+it "has the correct values" do
+  expect(fetch_colors(params)).to match_array(["blue", "green", "yellow"])
+end
+```
+
+This allows us to ensure that each side of the comparison has the same set
+values, irrespective of ordering.