Raise on bad values passed for retry counts

Prevent these from propogating away from where the issue happened.

Author: fhunleth

lib/i2c/i2c_dev.ex

@@ -51,6 +51,10 @@ defmodule Circuits.I2C.I2CDev do
   def open(bus_name, options) do
     retries = Keyword.get(options, :retries, 0)
 
+    if not (is_integer(retries) and retries >= 0) do
+      raise ArgumentError, "retries must be a non-negative integer"
+    end
+
     with {:ok, ref, flags} <- Nif.open(bus_name) do
       {:ok, %__MODULE__{ref: ref, flags: flags, retries: retries}}
     end

test/i2c/i2c_dev_test.exs

@@ -35,6 +35,11 @@ defmodule Circuits.I2CDevTest do
       assert {:ok, <<0x30, 0x31, 0x32, 0x33, 0x34>>} == Bus.read(i2c, 0x30, 5, [])
       Bus.close(i2c)
     end
+
+    test "bad retries caught" do
+      assert_raise ArgumentError, fn -> I2CDev.open("i2c-test-0", retries: -1) end
+      assert_raise ArgumentError, fn -> I2CDev.open("i2c-test-0", retries: nil) end
+    end
   end
 
   describe "read/4" do