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

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.