Refactor and migrate more functions out of api into app package (#5063)

app/user_test.go

@@ -0,0 +1,27 @@
+// Copyright (c) 2016 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package app
+
+import (
+	"testing"
+)
+
+func TestIsUsernameTaken(t *testing.T) {
+	th := Setup().InitBasic()
+	user := th.BasicUser
+	taken := IsUsernameTaken(user.Username)
+
+	if !taken {
+		t.Logf("the username '%v' should be taken", user.Username)
+		t.FailNow()
+	}
+
+	newUsername := "randomUsername"
+	taken = IsUsernameTaken(newUsername)
+
+	if taken {
+		t.Logf("the username '%v' should not be taken", newUsername)
+		t.FailNow()
+	}
+}