@@ -53,10 +53,12 @@ public static function generateEtagFromTables(array $tables, string $source = 'u
         // If the source is 'etag_version', use a cached version key as the source of truth.
         $lastUpdated = collect($tables)->map(function ($table) use ($source) {
             if ($source === 'etag_version') {
-                // This is not currently implemented but serves as a placeholder for future flexibility.
-                // The idea is to use a cached version key (e.g., "etag_version_table_name") as the source of truth.
-                // This would allow us to version the ETag dynamically and invalidate it using model observers or other mechanisms.
-                // If implemented, observers can increment this version key whenever the corresponding table is updated.
+                /**
+                 * This is not currently implemented but serves as a placeholder for future flexibility.
+                 * The idea is to use a cached version key (e.g., "etag_version_table_name") as the source of truth.
+                 * This would allow us to version the ETag dynamically and invalidate it using model observers or other mechanisms.
+                 * If implemented, observers can increment this version key whenever the corresponding table is updated.
+                 */
                 return Cache::get("etag_version_{$table}", 0);
             }
 
 
@@ -0,0 +1,65 @@
+<?php
+
+namespace ProcessMaker\Tests\Feature\Etag;
+
+use Illuminate\Foundation\Testing\WithFaker;
+use Illuminate\Support\Facades\Route;
+use ProcessMaker\Models\Process;
+use ProcessMaker\Models\User;
+use Tests\TestCase;
+
+class HandleEtagCacheInvalidationTest extends TestCase
+{
+    use WithFaker;
+
+    protected $faker;
+
+    private string $response = 'OK';
+
+    private const TEST_ROUTE = '/_test/etag-cache-invalidation';
+
+    public function setUp(): void
+    {
+        parent::setUp();
+
+        // Define a route with the etag middleware and etag_tables default.
+        Route::middleware('etag')
+            ->get(self::TEST_ROUTE, function () {
+                return response($this->response, 200);
+            })
+            ->defaults('etag_tables', 'processes');
+    }
+
+    public function testEtagInvalidatesOnDatabaseUpdate()
+    {
+        $user = User::factory()->create();
+        $this->actingAs($user);
+
+        // Create a process record to simulate database changes.
+        $process = Process::factory()->create([
+            'updated_at' => now()->yesterday(),
+        ]);
+
+        // First request: Get the initial ETag.
+        $response = $this->get(self::TEST_ROUTE);
+        $initialEtag = $response->headers->get('ETag');
+        $this->assertNotNull($initialEtag, 'Initial ETag was set');
+
+        // Simulate a database update by changing `updated_at`.
+        $process->update(['name' => $this->faker->name]);
+
+        // Second request: ETag should change due to the database update.
+        $responseAfterUpdate = $this->get(self::TEST_ROUTE);
+        $newEtag = $responseAfterUpdate->headers->get('ETag');
+
+        $this->assertNotNull($newEtag, 'New ETag was set after database update');
+        $this->assertNotEquals($initialEtag, $newEtag, 'ETag changed after database update');
+
+        // Third request: Simulate a client sending the old ETag.
+        $responseWithOldEtag = $this->withHeaders(['If-None-Match' => $initialEtag])
+            ->get(self::TEST_ROUTE);
+
+        $responseWithOldEtag->assertStatus(200);
+        $responseWithOldEtag->assertHeader('ETag', $newEtag, 'Response did not return the updated ETag');
+    }
+}
@@ -3,8 +3,7 @@
 namespace ProcessMaker\Tests\Feature\Etag;
 
 use Illuminate\Support\Facades\Route;
-use ProcessMaker\Http\Middleware\Etag\HandleEtag;
-use ProcessMaker\Http\Resources\Caching\EtagManager;
+use ProcessMaker\Models\Process;
 use ProcessMaker\Models\User;
 use Tests\TestCase;
 
@@ -19,7 +18,7 @@ public function setUp(): void
         parent::setUp();
 
         // Define a route that uses the HandleEtag middleware.
-        Route::middleware(HandleEtag::class)->any(self::TEST_ROUTE, function () {
+        Route::middleware('etag')->any(self::TEST_ROUTE, function () {
             return response($this->response, 200);
         });
     }
@@ -84,4 +83,32 @@ public function testDefaultGetEtagGeneratesCorrectEtagWithUser()
         $expectedEtag = '"' . md5($user->id . $this->response) . '"';
         $response->assertHeader('ETag', $expectedEtag);
     }
+
+    public function testReturns304NotModifiedWhenEtagMatchesTables()
+    {
+        $user = User::factory()->create();
+        $this->actingAs($user);
+
+        Process::factory()->create([
+            'updated_at' => now()->yesterday(),
+        ]);
+
+        Route::middleware('etag')->any(self::TEST_ROUTE, function () {
+            return response($this->response, 200);
+        })->defaults('etag_tables', 'processes');
+
+        // Initial request to get the ETAg.
+        $response = $this->get(self::TEST_ROUTE);
+        $etag = $response->headers->get('ETag');
+        $this->assertNotNull($etag, 'ETag should be set in the initial response');
+
+        // Perform a second request sending the `If-None-Match`.
+        $responseWithMatchingEtag = $this->withHeaders(['If-None-Match' => $etag])
+            ->get(self::TEST_ROUTE);
+
+        // Verify response is 304 Not Modified.
+        $responseWithMatchingEtag->assertStatus(304);
+        $this->assertEmpty($responseWithMatchingEtag->getContent(), 'Response content is not empty for 304 Not Modified');
+        $this->assertEquals($etag, $responseWithMatchingEtag->headers->get('ETag'), 'ETag does not match the client-provided If-None-Match');
+    }
 }