Add Assert An Exception Is Raised as an elixir til

README.md

@@ -7,7 +7,7 @@ variety of languages and technologies. These are things that don't really
 warrant a full blog post. These are mostly things I learn by pairing with
 smart people at [Hashrocket](http://hashrocket.com/).
 
-_444 TILs and counting..._
+_445 TILs and counting..._
 
 ---
 
@@ -82,6 +82,7 @@ _444 TILs and counting..._
 ### Elixir
 
 - [Append To A Keyword List](elixir/append-to-a-keyword-list.md)
+- [Assert An Exception Is Raised](elixir/assert-an-exception-is-raised.md)
 - [Create A Date With The Date Sigil](elixir/create-a-date-with-the-date-sigil.md)
 - [Execute Raw SQL In An Ecto Migration](elixir/execute-raw-sql-in-an-ecto-migration.md)
 - [Expose Internal Representation](elixir/expose-internal-representation.md)

elixir/assert-an-exception-is-raised.md

@@ -0,0 +1,27 @@
+# Assert An Exception Is Raised
+
+Elixir's [`ExUnit`](http://elixir-lang.org/docs.html) comes with a number of
+different ways to make assertions in your tests. One of those functions is
+[`assert_raise`](http://elixir-lang.org/docs/stable/ex_unit/ExUnit.Assertions.html#assert_raise/2)
+which allows you to test that a particular exception is raised when the
+given function is invoked.
+
+Using `assert_raise/2` looks something like this:
+
+```elixir
+assert_raise FunctionClauseError, fn ->
+  Enum.chunk([1,2,3], 0) == []
+end
+```
+
+The `assert_raise/3` form is also available which allows you to test both
+the type of exception and the resulting message.
+
+```elixir
+assert_raise FunctionClauseError, ~r/^no function clause matching/, fn ->
+  Enum.chunk([1,2,3], 0) == []
+end
+```
+
+Using the regex sigil for the second argument is generally a good way to go
+to keep tests from getting too brittle.