diff --git a/lib/ai/formula_screen.dart b/lib/ai/formula_screen.dart
index dc1089f..6535ae5 100644
--- a/lib/ai/formula_screen.dart
+++ b/lib/ai/formula_screen.dart
@@ -63,10 +63,10 @@ class D4rtEditingController extends TextEditingController {
     if( _validateAsD4rtExpression(text) && _lastValue is StringResult ){
       return true;
     }
-    if( _validateAsD4rtExpression('"' + text + '"') && _lastValue is StringResult ){
+    if( _validateAsD4rtExpression('"$text"') && _lastValue is StringResult ){
       return true;
     }    
-    if( _validateAsD4rtExpression("'" + text + "'") && _lastValue is StringResult ){
+    if( _validateAsD4rtExpression("'$text'") && _lastValue is StringResult ){
       return true;
     }
     return false;
diff --git a/test/dart_test.dart b/test/dart_test.dart
index 9e78acc..ccedad0 100644
--- a/test/dart_test.dart
+++ b/test/dart_test.dart
@@ -1,6 +1,5 @@
 import 'package:test/test.dart';
 import 'package:d4rt/d4rt.dart';
-import 'dart:math' as Math;
 
 
 void main(){
diff --git a/test/database_test.dart b/test/database_test.dart
index e3541e7..c38e774 100644
--- a/test/database_test.dart
+++ b/test/database_test.dart
@@ -1,5 +1,4 @@
 import 'package:flutter_test/flutter_test.dart';
-import 'package:d4rt_formulas/database/database_service.dart';
 import 'package:d4rt_formulas/service_locator.dart';
 
 void main() {
diff --git a/test/physics_trigonometry_formulas_test.dart b/test/physics_trigonometry_formulas_test.dart
index 2b606f8..d3e3171 100644
--- a/test/physics_trigonometry_formulas_test.dart
+++ b/test/physics_trigonometry_formulas_test.dart
@@ -2,7 +2,6 @@ import 'package:d4rt_formulas/corpus.dart';
 import 'package:d4rt_formulas/defaults/default_corpus.dart';
 import 'package:d4rt_formulas/formula_evaluator.dart';
 import 'package:flutter_test/flutter_test.dart';
-import 'package:d4rt_formulas/formula_models.dart';
 
 void main() {
   TestWidgetsFlutterBinding.ensureInitialized();