diff --git a/app/Controllers/Test/TestsController.php b/app/Controllers/Test/TestsController.php
index 4b9e5a0..b4e5f83 100755
--- a/app/Controllers/Test/TestsController.php
+++ b/app/Controllers/Test/TestsController.php
@@ -50,7 +50,7 @@ class TestsController extends BaseController
             'isVisibleRpt' => $this->request->getGet('isVisibleRpt'),
             'TestSiteName' => $this->request->getGet('TestSiteName'),
             'TestSiteCode' => $this->request->getGet('TestSiteCode'),
-            'DepartmentID' => $this->request->getGet('DepartmentID'),
+            'DisciplineID' => $this->request->getGet('DisciplineID'),
             'search' => $search,
         ];
 
diff --git a/app/Models/Test/TestDefSiteModel.php b/app/Models/Test/TestDefSiteModel.php
index 69f8407..9f049dd 100755
--- a/app/Models/Test/TestDefSiteModel.php
+++ b/app/Models/Test/TestDefSiteModel.php
@@ -79,7 +79,7 @@ class TestDefSiteModel extends BaseModel {
   }
 
   /**
-   * Get tests list with discipline and department info
+   * Get tests list with discipline info
    */
   public function getTestsWithRelations($filters = []) {
     $builder = $this->db->table('testdefsite')
@@ -120,8 +120,8 @@ class TestDefSiteModel extends BaseModel {
       $builder->like('testdefsite.TestSiteCode', $filters['TestSiteCode']);
     }
 
-    if (!empty($filters['DepartmentID'])) {
-      $builder->where('COALESCE(testdefsite.DepartmentID, cal.DepartmentID)', $filters['DepartmentID']);
+    if (!empty($filters['DisciplineID'])) {
+      $builder->where('COALESCE(testdefsite.DisciplineID, cal.DisciplineID)', $filters['DisciplineID']);
     }
 
     if (!empty($filters['search'])) {
diff --git a/public/api-docs.bundled.yaml b/public/api-docs.bundled.yaml
index 23a0a1f..e42cbac 100755
--- a/public/api-docs.bundled.yaml
+++ b/public/api-docs.bundled.yaml
@@ -4696,11 +4696,11 @@ paths:
           schema:
             type: integer
           description: Filter by site ID
-        - name: DepartmentID
+        - name: DisciplineID
           in: query
           schema:
             type: integer
-          description: Filter by department ID
+          description: Filter by discipline ID
         - name: TestType
           in: query
           schema:
diff --git a/public/paths/tests.yaml b/public/paths/tests.yaml
index 950c395..a8673f7 100755
--- a/public/paths/tests.yaml
+++ b/public/paths/tests.yaml
@@ -22,11 +22,11 @@
         schema:
           type: integer
         description: Filter by site ID
-      - name: DepartmentID
+      - name: DisciplineID
         in: query
         schema:
           type: integer
-        description: Filter by department ID
+        description: Filter by discipline ID
       - name: TestType
         in: query
         schema:
diff --git a/tests/feature/Test/TestIndexFilterTest.php b/tests/feature/Test/TestIndexFilterTest.php
new file mode 100644
index 0000000..3435075
--- /dev/null
+++ b/tests/feature/Test/TestIndexFilterTest.php
@@ -0,0 +1,55 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Feature\Test;
+
+use App\Models\Test\TestDefSiteModel;
+use CodeIgniter\Test\CIUnitTestCase;
+use CodeIgniter\Test\FeatureTestTrait;
+
+class TestIndexFilterTest extends CIUnitTestCase
+{
+    use FeatureTestTrait;
+
+    public function testIndexFiltersByDisciplineId(): void
+    {
+        $disciplineId = $this->findActiveDisciplineId();
+        if ($disciplineId === null) {
+            $this->markTestSkipped('No active test record with discipline found.');
+        }
+
+        $response = $this->call('get', 'api/test?DisciplineID=' . $disciplineId);
+        $response->assertStatus(200);
+
+        $json = json_decode($response->getJSON(), true);
+        $rows = $json['data'] ?? [];
+
+        $this->assertNotEmpty($rows);
+
+        foreach ($rows as $row) {
+            $rowDisciplineId = (int) ($row['DisciplineID'] ?? 0);
+            $this->assertSame($disciplineId, $rowDisciplineId);
+        }
+    }
+
+    private function findActiveDisciplineId(): ?int
+    {
+        $model = new TestDefSiteModel();
+
+        $row = $model->db->table('testdefsite')
+            ->select('COALESCE(testdefsite.DisciplineID, cal.DisciplineID) AS DisciplineID')
+            ->join('testdefcal cal', 'cal.TestSiteID = testdefsite.TestSiteID AND cal.EndDate IS NULL', 'left')
+            ->where('testdefsite.EndDate IS NULL')
+            ->where('COALESCE(testdefsite.DisciplineID, cal.DisciplineID) IS NOT NULL', null, false)
+            ->orderBy('testdefsite.TestSiteID', 'ASC')
+            ->get()
+            ->getRowArray();
+
+        if (!$row || !isset($row['DisciplineID'])) {
+            return null;
+        }
+
+        return (int) $row['DisciplineID'];
+    }
+}