问题
I have a function in Elixir that produces three random RGB tuples in a list.
defmodule Color do
@doc """
Create three random r,g,b colors as a list of three tuples
## Examples
iex> colors = Color.pick_color()
iex> colors
[{207, 127, 117}, {219, 121, 237}, {109, 101, 206}]
"""
def pick_color() do
color = Enum.map((0..2), fn(x)->
r = Enum.random(0..255)
g = Enum.random(0..255)
b = Enum.random(0..255)
{r, g, b}
end)
end
When I run my tests, my doctests fail. The resulting list of tuples are different than what is defined in my doctest. How can I write a doctest for a function that returns a random value?
回答1:
In order to test a function with doctests, you must be able to predict the output of your function. In this case, you can't predict the output of your function.
However you could test your function with regular tests.
Here is a test that would make sure Color.pick_color()
produces a list of 3 tuples, using pattern matching:
test "pick color" do
[{_, _, _}, {_, _, _}, {_, _, _}] = Color.pick_color()
end
You could also check if each value is between 0
and 255
, etc.
回答2:
You can make the random functions deterministic by setting the seed of :rand
's random number generator. This is also how Enum.random/1 is tested in Elixir.
First, open iex
and set the seed of the current process to any value:
iex> :rand.seed(:exsplus, {101, 102, 103})
Then, run your function in iex
iex> Color.pick_color()
Now just copy this value into your doctest along with the :rand.seed
call. By explicitly setting the seed, you're going to get the same values from the functions in :rand
module and Enum.random/1
uses :rand
internally.
iex(1)> :rand.seed(:exsplus, {1, 2, 3})
iex(2)> for _ <- 1..10, do: Enum.random(1..10)
[4, 3, 8, 1, 6, 8, 1, 6, 7, 7]
iex(3)> :rand.seed(:exsplus, {1, 2, 3})
iex(4)> for _ <- 1..10, do: Enum.random(1..10)
[4, 3, 8, 1, 6, 8, 1, 6, 7, 7]
iex(5)> :rand.seed(:exsplus, {1, 2, 3})
iex(6)> for _ <- 1..10, do: Enum.random(1..10)
[4, 3, 8, 1, 6, 8, 1, 6, 7, 7]
来源:https://stackoverflow.com/questions/48857468/elixir-doctest-fails-for-function-that-returns-random-values