Resolve binary command's path to be absolute

config/config.exs

@@ -8,6 +8,7 @@ use Mix.Config
 # * udhcpd_handler: capture whatever happens with udhcpd
 # * interface_renamer: capture interfaces that get renamed
 # * resolvconf: don't update the real resolv.conf
+# * path: limit search for tools to our test harness
 # * persistence_dir: use the current directory
 # * power_managers: register a manager for test0 so that tests
 #      that need to validate power management calls can use it.
@@ -21,6 +22,7 @@ config :vintage_net,
   udhcpd_handler: VintageNetTest.CapturingUdhcpdHandler,
   interface_renamer: VintageNetTest.CapturingInterfaceRenamer,
   resolvconf: "/dev/null",
+  path: "#{File.cwd!()}/test/fixtures/root/bin",
   persistence_dir: "./test_tmp/persistence",
   power_managers: [
     {VintageNetTest.TestPowerManager, [ifname: "test0", watchdog_timeout: 50]},

lib/vintage_net/command.ex

@@ -6,15 +6,15 @@ defmodule VintageNet.Command do
   def cmd(command, args, opts \\ []) when is_binary(command) do
     new_opts = force_path_env(opts)
 
-    System.cmd(command, args, new_opts)
+    System.cmd(find_executable!(command), args, new_opts)
   end
 
   @spec muon_cmd(Path.t(), [binary()], keyword()) ::
           {Collectable.t(), exit_status :: non_neg_integer()}
   def muon_cmd(command, args, opts \\ []) when is_binary(command) do
     new_opts = opts |> force_path_env() |> add_muon_options()
 
-    MuonTrap.cmd(command, args, new_opts)
+    MuonTrap.cmd(find_executable!(command), args, new_opts)
   end
 
   @doc """
@@ -28,15 +28,32 @@ defmodule VintageNet.Command do
     )
   end
 
+  defp find_executable!(command) do
+    find_executable(command) ||
+      raise(RuntimeError, "Can't find '#{command}' in '#{path_env()}'")
+  end
+
+  defp find_executable(command) do
+    paths = String.split(path_env(), ":")
+
+    Enum.find_value(paths, fn path ->
+      full_path = Path.join(path, command)
+
+      if File.exists?(full_path) do
+        full_path
+      end
+    end)
+  end
+
   defp force_path_env(opts) do
     original_env = Keyword.get(opts, :env, [])
 
-    new_env = [path_env() | List.keydelete(original_env, "PATH", 0)]
+    new_env = [{"PATH", path_env()} | List.keydelete(original_env, "PATH", 0)]
 
     Keyword.put(opts, :env, new_env)
   end
 
   defp path_env() do
-    {"PATH", Application.get_env(:vintage_net, :path)}
+    Application.get_env(:vintage_net, :path)
   end
 end

test/fixtures/root/bin/echo

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+/bin/echo "$@"

test/fixtures/root/bin/false

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+exit 1

test/fixtures/root/bin/ip

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+exit 1

test/fixtures/root/bin/rm

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+/bin/rm "$@"

test/fixtures/root/bin/sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+/bin/sh "$@"

test/fixtures/root/bin/sleep

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+/bin/sleep "$@"

test/fixtures/root/bin/test

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+/bin/test "$@"

test/fixtures/root/bin/touch

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+/usr/bin/touch "$@"

test/vintage_net/interface_test.exs

@@ -227,12 +227,12 @@ defmodule VintageNet.InterfaceTest do
             {"run.sh",
              """
              #!/bin/sh
-             if [ -e first_try ]; then
+             if test -e first_try; then
                touch i_am_configured
              else
                # Hang the first time
                touch first_try
-               /bin/sleep 10000
+               sleep 10000
                echo "Should not get here"
              fi
              """}