diff --git a/catmodel/mixedraschbirnbaum/tests/mixedraschbirnbaum_test.php b/catmodel/mixedraschbirnbaum/tests/mixedraschbirnbaum_test.php
index c4fc4dfd4..847100c6c 100644
--- a/catmodel/mixedraschbirnbaum/tests/mixedraschbirnbaum_test.php
+++ b/catmodel/mixedraschbirnbaum/tests/mixedraschbirnbaum_test.php
@@ -58,12 +58,17 @@ public function test_calculate_params_returns_expected_values($itemresponse, arr
         $this->assertEqualsWithDelta($expected['guessing'], $result['guessing'], 0.0001);
     }
 
+    /**
+     * Data provider for test_calculate_params_returns_expected_values
+     *
+     * @return array
+     */
     public static function calculate_params_returns_expected_values_provider(): array {
         return [
-                [
-                    'itemresponse' => [new model_item_response(0.3, (new model_person_param(1))->set_ability(0.2))],
+            'first' => [
+                    'itemresponse' => [new model_item_response(0.3, (new model_person_param(1, 1))->set_ability(0.2))],
                     'expected' => ['difficulty' => 1.2041, 'discrimination' => 3.0, 'guessing' => 0.0],
-                ]
+            ],
         ];
     }
 
diff --git a/catmodel/rasch/tests/rasch_test.php b/catmodel/rasch/tests/rasch_test.php
index 2a25c1c1d..a7b244ec6 100644
--- a/catmodel/rasch/tests/rasch_test.php
+++ b/catmodel/rasch/tests/rasch_test.php
@@ -57,12 +57,17 @@ public function test_calculate_params_returns_expected_values($itemresponse, arr
         $this->assertEqualsWithDelta($expected['difficulty'], $result['difficulty'], 0.0001);
     }
 
+    /**
+     * Data provider for test_calculate_params_returns_expected_values
+     *
+     * @return array
+     */
     public static function calculate_params_returns_expected_values_provider(): array {
         return [
                 [
-                    'itemresponse' => [new model_item_response(0.3, (new model_person_param(1))->set_ability(0.2))],
+                    'itemresponse' => [new model_item_response(0.3, (new model_person_param(1, 1))->set_ability(0.2))],
                     'expected' => ['difficulty' => 5.5],
-                ]
+                ],
         ];
     }
 
diff --git a/catmodel/raschbirnbaum/tests/raschbirnbaum_test.php b/catmodel/raschbirnbaum/tests/raschbirnbaum_test.php
index 5257e47d0..e30461bb8 100644
--- a/catmodel/raschbirnbaum/tests/raschbirnbaum_test.php
+++ b/catmodel/raschbirnbaum/tests/raschbirnbaum_test.php
@@ -58,12 +58,17 @@ public function test_calculate_params_returns_expected_values($itemresponse, arr
         $this->assertEqualsWithDelta($expected['discrimination'], $result['discrimination'], 0.0001);
     }
 
+    /**
+     * Data provider for test_calculate_params_returns_expected_values
+     *
+     * @return array
+     */
     public static function calculate_params_returns_expected_values_provider(): array {
         return [
                 [
-                    'itemresponse' => [new model_item_response(0.3, (new model_person_param(1))->set_ability(0.2))],
+                    'itemresponse' => [new model_item_response(0.3, (new model_person_param(1, 1))->set_ability(0.2))],
                     'expected' => ['difficulty' => 1.4974, 'discrimination' => 3.0],
-                ]
+                ],
         ];
     }
 
diff --git a/classes/catcalc.php b/classes/catcalc.php
index 1acc08771..ae1aaecf0 100644
--- a/classes/catcalc.php
+++ b/classes/catcalc.php
@@ -203,13 +203,13 @@ public static function estimate_item_params(array $itemresponse, model_model $mo
     /**
      * Builds the jacobian function for item params and the given model.
      *
-     * @param array<model_item_response> $itemresponse
+     * @param array $itemresponse
      * @param catcalc_item_estimator $model
      *
      * @return mixed
      *
      */
-    public static function build_itemparam_jacobian(array $itemresponse, catcalc_item_estimator $model) {
+    public static function build_itemparam_jacobian(array $itemresponse, catcalc_item_estimator $model): mixed {
         // Define Jacobi vector (1st derivative) of the Log Likelihood.
         $funs = [];
 
diff --git a/tests/catcalc_test.php b/tests/catcalc_test.php
index db86c69eb..591a4084e 100644
--- a/tests/catcalc_test.php
+++ b/tests/catcalc_test.php
@@ -31,6 +31,7 @@
 use Exception;
 use local_catquiz\local\model\model_item_param;
 use local_catquiz\local\model\model_item_param_list;
+use local_catquiz\local\model\model_model;
 use local_catquiz\local\model\model_responses;
 use moodle_exception;
 use SebastianBergmann\RecursionContext\InvalidArgumentException;
@@ -147,7 +148,7 @@ public static function simulation_steps_calculated_ability_provider(): array {
     public function test_build_item_param_jacobian() {
         $itemresponse = [];
         $mr = new model_responses();
-        $model = new raschbirnbaum($mr, 'raschbirnbaum');
+        $model = model_model::get_instance('raschbirnbaum');
         $this->assertEquals(fn () => 'b', catcalc::build_itemparam_jacobian($itemresponse, $model));
     }
 
diff --git a/tests/lib.php b/tests/lib.php
index 18972c369..16382de46 100644
--- a/tests/lib.php
+++ b/tests/lib.php
@@ -69,9 +69,10 @@ function loadresponsesforperson($filename, $person = 0): array {
  *
  * @param string $filename The file to load the responses from.
  * @param string $label  The label of the item.
+ * @param string $scale
  * @return model_responses
  */
-function loadresponsesforitem($filename, $label, $scale = 'Gesamt'): model_responses {
+function loadresponsesforitem(string $filename, string $label, string $scale = 'Gesamt'): model_responses {
     global $CFG;
     if (($handle = fopen($filename, "r")) === false) {
         throw new UnexpectedValueException("Can not open file: " . $filename);
@@ -107,6 +108,7 @@ function loadresponsesforitem($filename, $label, $scale = 'Gesamt'): model_respo
  * model_person_param object.
  *
  * @param string $filename
+ * @param string $scale
  * @return model_person_param_list
  * @throws UnexpectedValueException
  */