✅ Fix flaky tests (#113)

For a while now, I've been seeing spurious test failures, but hadn't been able to figure out the root cause.

It turns out that clearing the entire `InMemoryCache` before tests was causing test interference. This is obvious in retrospect.

There's also a spurious failure in CI with the integration tests where a second instance tries to start with the same SDK key as another. I'm not sure if I've fixed that one with these changes.

Changes:
- Clear only a specific cache key from the InMemoryCache, and only when multiple tests will use the same key.
- Mark the integration tests as `async: false` to be sure they run in isolation.
- Eliminate log noise from the tests.

lib/config_cat/in_memory_cache.ex

@@ -22,9 +22,9 @@ defmodule ConfigCat.InMemoryCache do
     GenServer.call(__MODULE__, {:set, cache_key, value})
   end
 
-  @spec clear :: :ok
-  def clear do
-    GenServer.call(__MODULE__, :clear)
+  @spec clear(ConfigCache.key()) :: :ok
+  def clear(cache_key) do
+    GenServer.call(__MODULE__, {:clear, cache_key})
   end
 
   @impl GenServer
@@ -33,8 +33,8 @@ defmodule ConfigCat.InMemoryCache do
   end
 
   @impl GenServer
-  def handle_call(:clear, _from, _state) do
-    {:reply, :ok, %{}}
+  def handle_call({:clear, cache_key}, _from, state) do
+    {:reply, :ok, Map.delete(state, cache_key)}
   end
 
   @impl GenServer

test/config_cat/in_memory_cache_test.exs

@@ -1,34 +1,34 @@
 defmodule ConfigCat.InMemoryCacheTest do
   use ExUnit.Case, async: true
 
-  alias ConfigCat.InMemoryCache, as: Cache
+  alias ConfigCat.InMemoryCache
 
   @cache_key "CACHE_KEY"
 
   setup do
-    Cache.clear()
+    InMemoryCache.clear(@cache_key)
 
     :ok
   end
 
   test "cache is initially empty" do
-    assert Cache.get(@cache_key) == {:error, :not_found}
+    assert InMemoryCache.get(@cache_key) == {:error, :not_found}
   end
 
   test "returns cached value" do
     entry = "serialized-cache-entry"
 
-    :ok = Cache.set(@cache_key, entry)
+    :ok = InMemoryCache.set(@cache_key, entry)
 
-    assert {:ok, ^entry} = Cache.get(@cache_key)
+    assert {:ok, ^entry} = InMemoryCache.get(@cache_key)
   end
 
   test "cache is empty after clearing" do
     entry = "serialized-cache-entry"
 
-    :ok = Cache.set(@cache_key, entry)
+    :ok = InMemoryCache.set(@cache_key, entry)
 
-    assert :ok = Cache.clear()
-    assert Cache.get(@cache_key) == {:error, :not_found}
+    assert :ok = InMemoryCache.clear(@cache_key)
+    assert InMemoryCache.get(@cache_key) == {:error, :not_found}
   end
 end

test/config_cat_test.exs

@@ -114,6 +114,7 @@ defmodule ConfigCatTest do
              } = ConfigCat.get_value_details("testStringKey", "", user, client: client)
     end
 
+    @tag capture_log: true
     test "get_all_value_details/2 returns evaluation details for all keys", %{client: client} do
       all_details = ConfigCat.get_all_value_details(client: client)
       details_by_key = fn key -> Enum.find(all_details, &(&1.key == key)) end
@@ -133,6 +134,8 @@ defmodule ConfigCatTest do
   end
 
   describe "when the configuration has not been fetched" do
+    @describetag capture_log: true
+
     setup do
       {:ok, client} = start_client()
 

test/integration_test.exs

@@ -1,6 +1,10 @@
 defmodule ConfigCat.IntegrationTest do
-  use ExUnit.Case, async: true
+  # Must be async: false to avoid a collision with other tests.
+  # Now that we only allow a single ConfigCat instance to use the same SDK key,
+  # one of the async tests would fail due to the existing running instance.
+  use ExUnit.Case, async: false
 
+  alias ConfigCat.Cache
   alias ConfigCat.CachePolicy
   alias ConfigCat.InMemoryCache
 
@@ -16,6 +20,7 @@ defmodule ConfigCat.IntegrationTest do
     |> assert_sdk_key_required()
   end
 
+  @tag capture_log: true
   test "raises error when starting another instance with the same SDK key" do
     {:ok, _} = start_config_cat(@sdk_key, name: :original)
 
@@ -108,7 +113,9 @@ defmodule ConfigCat.IntegrationTest do
   end
 
   defp start_config_cat(sdk_key, options \\ []) do
-    InMemoryCache.clear()
+    sdk_key
+    |> Cache.generate_key()
+    |> InMemoryCache.clear()
 
     name = UUID.uuid4() |> String.to_atom()
     default_options = [name: name, sdk_key: sdk_key]

test/support/cache_policy_case.ex

@@ -85,7 +85,6 @@ defmodule ConfigCat.CachePolicyCase do
 
   defp start_cache(instance_id) do
     cache_key = UUID.uuid4()
-    InMemoryCache.clear()
 
     {:ok, _pid} =
       start_supervised(