Today I Learned

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Assert An Exception Is Raised

Elixir's ExUnit comes with a number of different ways to make assertions in your tests. One of those functions is assert_raise 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:

assert_raise FunctionClauseError, fn ->
  Enum.chunk([1,2,3], 0)

The assert_raise/3 form is also available which allows you to test both the type of exception and the resulting message.

assert_raise FunctionClauseError, ~r/^no function clause matching/, fn ->
  Enum.chunk([1,2,3], 0)

Using the regex sigil for the second argument is generally a good way to go to keep tests from getting too brittle.

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