test: add assertion testing if value passes eventually

test/supavisor/prom_ex_test.exs

@@ -2,6 +2,8 @@ defmodule Supavisor.PromExTest do
   use ExUnit.Case, async: true
   use Supavisor.DataCase
 
+  import Supavisor.Asserts
+
   alias Supavisor.Monitoring.PromEx
 
   @tenant "prom_tenant"
@@ -33,7 +35,7 @@ defmodule Supavisor.PromExTest do
 
     Process.sleep(3000)
 
-    refute PromEx.get_metrics() =~ "tenant=\"#{@tenant}\""
+    refute_eventually(fn -> PromEx.get_metrics() =~ "tenant=\"#{@tenant}\"" end)
   end
 
   test "clean_string/1 removes extra spaces from metric string" do

test/support/asserts.ex

@@ -0,0 +1,41 @@
+defmodule Supavisor.Asserts do
+  @doc """
+  Asserts that `function` will eventually success. Fails otherwise.
+
+  It performs `repeats` checks with `delay` milliseconds between each check.
+  """
+  def assert_eventually(repeats \\ 5, delay \\ 1000, function)
+
+  def assert_eventually(0, _, _) do
+    raise ExUnit.AssertionError, message: "Expected function to return truthy value"
+  end
+
+  def assert_eventually(n, delay, func) do
+    if func.() do
+      :ok
+    else
+      Process.sleep(delay)
+      assert_eventually(n - 1, delay, func)
+    end
+  end
+
+  @doc """
+  Asserts that `function` will eventually fail. Fails otherwise.
+
+  It performs `repeats` checks with `delay` milliseconds between each check.
+  """
+  def refute_eventually(repeats \\ 5, delay \\ 1000, function)
+
+  def refute_eventually(0, _, _) do
+    raise ExUnit.AssertionError, message: "Expected function to return falsey value"
+  end
+
+  def refute_eventually(n, delay, func) do
+    if func.() do
+      Process.sleep(delay)
+      refute_eventually(n - 1, delay, func)
+    else
+      :ok
+    end
+  end
+end