Add basic unittests for the config related functionality

config/testdata/valid-config.json

@@ -0,0 +1,63 @@
+{
+  "_": "This is your OONI Probe config file. See https://ooni.io/help/probe-cli for help",
+  "_version": 0,
+  "_informed_consent": false,
+  "auto_update": true,
+  "sharing": {
+    "include_ip": false,
+    "include_asn": true,
+    "include_gps": true,
+    "upload_results": true,
+    "send_crash_reports": true
+  },
+  "notifications": {
+    "enabled": true,
+    "notify_on_test_completion": true,
+    "notify_on_news": false
+  },
+  "automated_testing": {
+    "enabled": false,
+    "enabled_tests": [
+      "web-connectivity",
+      "facebook-messenger",
+      "whatsapp",
+      "telegram",
+      "dash",
+      "ndt",
+      "http-invalid-request-line",
+      "http-header-field-manipulation"
+    ],
+    "monthly_allowance": "300MB"
+  },
+  "test_settings": {
+    "websites": {
+      "enabled_categories": []
+    },
+    "instant_messaging": {
+      "enabled_tests": [
+        "facebook-messenger",
+        "whatsapp",
+        "telegram"
+      ]
+    },
+    "performance": {
+      "enabled_tests": [
+        "ndt"
+      ],
+      "ndt_server": "auto",
+      "ndt_server_port": "auto",
+      "dash_server": "auto",
+      "dash_server_port": "auto"
+    },
+    "middlebox": {
+      "enabled_tests": [
+        "http-invalid-request-line",
+        "http-header-field-manipulation"
+      ]
+    }
+  },
+  "advanced": {
+    "include_country": true,
+    "use_domain_fronting": false
+  }
+}