Fix UniFi app test() method to properly validate credentials

The test() method was using appTest() which only checked HTTP status codes,
causing false "Invalid credentials" errors even when credentials were valid.
This fix aligns the test() method with the working livestats() approach.

Changes:
- Use execute() directly with explicit POST method (same as livestats)
- Handle HTTP 400 errors for self-hosted controller auth failures
- Handle HTTP 401/403 errors for UDM auth failures
- Validate self-hosted response body (meta.rc === "ok")
- Verify login by fetching stats to confirm session is valid
- Provide descriptive error messages for different failure scenarios

Fixes #640, #695, #811

Author: jaycollett

UniFi/UniFi.php

@@ -20,12 +20,74 @@ public function __construct()
     public function test()
     {
         $urls = $this->getAPIURLs();
-        $test = parent::appTest(
+        $self_hosted = $this->getConfigValue("self_hosted", false);
+
+        // Perform login request
+        $loginRes = parent::execute(
             $this->url($urls['loginURL']),
             $this->getLoginAttributes(),
+            null,
+            'POST'
         );
 
-        echo $test->status;
+        if ($loginRes === null) {
+            echo "Failed: Connection error";
+            return;
+        }
+
+        $statusCode = $loginRes->getStatusCode();
+        $body = json_decode($loginRes->getBody());
+
+        // Check for explicit failure codes
+        if ($statusCode === 401 || $statusCode === 403) {
+            echo "Failed: Invalid credentials";
+            return;
+        }
+
+        // Self-hosted controllers return 400 on auth failure
+        if ($statusCode === 400) {
+            $msg = isset($body->meta->msg) ? $body->meta->msg : "Invalid credentials";
+            echo "Failed: " . $msg;
+            return;
+        }
+
+        // For 200 responses, verify the login actually succeeded
+        if ($statusCode === 200) {
+            // Self-hosted: check meta.rc === "ok"
+            if ($self_hosted) {
+                if (!isset($body->meta->rc) || $body->meta->rc !== "ok") {
+                    $msg = isset($body->meta->msg) ? $body->meta->msg : "Login failed";
+                    echo "Failed: " . $msg;
+                    return;
+                }
+            }
+
+            // Additional verification: try to fetch stats to confirm session works
+            $statsRes = parent::execute(
+                $this->url($urls['statsURL']),
+                $this->getAttributes(),
+                null,
+                'GET'
+            );
+
+            if ($statsRes !== null && $statsRes->getStatusCode() === 200) {
+                $statsBody = json_decode($statsRes->getBody());
+                // UDM returns data array, self-hosted returns meta.rc
+                $hasData = isset($statsBody->data);
+                $hasMetaOk = isset($statsBody->meta) && isset($statsBody->meta->rc) && $statsBody->meta->rc === "ok";
+                if ($hasData || $hasMetaOk) {
+                    echo "Successfully connected to UniFi";
+                    return;
+                }
+            }
+
+            // Stats fetch failed but login seemed ok
+            echo "Login succeeded but unable to fetch stats - check user permissions";
+            return;
+        }
+
+        // Unexpected status code
+        echo "Failed: Unexpected response (HTTP " . $statusCode . ")";
     }
 
     public function livestats()