Prefer test config from environment

Author: Denis-Averin

lib/src/configuration.dart

@@ -75,10 +75,14 @@ class Configuration {
   }
 
   /// Load configuration from environment variables
-  static fromEnv({String prefix = ""}) {
-    final accessToken = Platform.environment["${prefix}ACCESS_TOKEN"];
-    return Configuration(
-      accessToken: accessToken,
-    );
+  static Configuration? fromEnv({String prefix = ""}) {
+    final String? accessToken = Platform.environment["${prefix}ACCESS_TOKEN"];
+    if (accessToken != null && accessToken.isNotEmpty) {
+      return Configuration(
+        accessToken: accessToken,
+      );
+    }
+
+    return null;
   }
 }

test/test_config.dart

@@ -4,10 +4,11 @@ import 'dart:math';
 import 'package:aspose_barcode_cloud/aspose_barcode_cloud.dart';
 
 class TestConfig {
-  static final configuration =
-      Configuration.load("test${Platform.pathSeparator}configuration.json") ??
-          Configuration.fromEnv(prefix: "TEST_CONFIGURATION_");
-  static final apiClient = ApiClient(configuration);
+  static final Configuration? configuration =
+      Configuration.fromEnv(prefix: "TEST_CONFIGURATION_") ??
+          Configuration.load("test${Platform.pathSeparator}configuration.json");
+
+  static final apiClient = ApiClient(configuration!);
 
   static final barcodeApi = BarcodeApi(apiClient);