diff --git a/pkg/storage/file/fstore.go b/pkg/storage/file/fstore.go
index 82358f4..fec6afe 100644
--- a/pkg/storage/file/fstore.go
+++ b/pkg/storage/file/fstore.go
@@ -326,5 +326,9 @@ func readDirNames(elem ...string) ([]string, error) {
 	if err != nil {
 		return nil, err
 	}
+	defer func() {
+		_ = f.Close()
+	}()
+
 	return f.Readdirnames(0)
 }
diff --git a/pkg/test/storage_suite.go b/pkg/test/storage_suite.go
index 3050054..e0e1ba0 100644
--- a/pkg/test/storage_suite.go
+++ b/pkg/test/storage_suite.go
@@ -147,22 +147,19 @@ func testContent(t *testing.T, store storage.Store, extHost *extension.Host) {
 		Reader: bytes.NewReader(content),
 	}
 	id, err := store.AddMessage(delivery)
-	if err != nil {
-		t.Fatal(err)
-	}
-	// Get and check.
+	require.NoError(t, err, "AddMessage() failed")
+
+	// Read stored message source.
 	m, err := store.GetMessage(mailbox, id)
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err, "GetMessage() failed")
 	r, err := m.Source()
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err, "Source() failed")
 	got, err := io.ReadAll(r)
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err, "failed to read source")
+	err = r.Close()
+	assert.NoError(t, err, "failed to close source reader")
+
+	// Verify source.
 	if len(got) != len(content) {
 		t.Errorf("Got len(content) == %v, want: %v", len(got), len(content))
 	}
@@ -412,26 +409,27 @@ func testNoMsgCap(t *testing.T, store storage.Store, extHost *extension.Host) {
 // testVisitMailboxes creates some mailboxes and confirms the VisitMailboxes method visits all of
 // them.
 func testVisitMailboxes(t *testing.T, ds storage.Store, extHost *extension.Host) {
+	// Deliver 2 test messages to each of 5 mailboxes.
 	boxes := []string{"abby", "bill", "christa", "donald", "evelyn"}
 	for _, name := range boxes {
 		DeliverToStore(t, ds, name, "Old Message", time.Now().Add(-24*time.Hour))
 		DeliverToStore(t, ds, name, "New Message", time.Now())
 	}
-	seen := 0
+
+	// Verify message and mailbox counts.
+	nboxes := 0
 	err := ds.VisitMailboxes(func(messages []storage.Message) bool {
-		seen++
-		count := len(messages)
-		if count != 2 {
-			t.Errorf("got: %v messages, want: 2", count)
+		nboxes++
+		name := "unknown"
+		if len(messages) > 0 {
+			name = messages[0].Mailbox()
 		}
+
+		assert.Equal(t, 2, len(messages), "incorrect message count in mailbox %s", name)
 		return true
 	})
-	if err != nil {
-		t.Error(err)
-	}
-	if seen != 5 {
-		t.Errorf("saw %v messages in total, want: 5", seen)
-	}
+	assert.NoError(t, err, "VisitMailboxes() failed")
+	assert.Equal(t, 5, nboxes, "visited %v mailboxes, want: 5", nboxes)
 }
 
 // DeliverToStore creates and delivers a message to the specific mailbox, returning the size of the