diff --git a/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java b/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
index 84c04f21..6cbca41e 100644
--- a/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -6,6 +6,7 @@
  * und dessen Bildschirm bis zu zehn Ziffern plus einem Dezimaltrennzeichen darstellen kann.
  * Enthält mit Absicht noch diverse Bugs oder unvollständige Funktionen.
  */
+//Kardeena Kameran
 public class Calculator {
 
     private String screen = "0";
@@ -118,16 +119,23 @@ public void pressNegativeKey() {
      * und das Ergebnis direkt angezeigt.
      */
     public void pressEqualsKey() {
+        if (latestOperation.isEmpty()) {
+            return;
+        }
         var result = switch(latestOperation) {
             case "+" -> latestValue + Double.parseDouble(screen);
             case "-" -> latestValue - Double.parseDouble(screen);
             case "x" -> latestValue * Double.parseDouble(screen);
             case "/" -> latestValue / Double.parseDouble(screen);
             default -> throw new IllegalArgumentException();
+
         };
         screen = Double.toString(result);
         if(screen.equals("Infinity")) screen = "Error";
         if(screen.endsWith(".0")) screen = screen.substring(0,screen.length()-2);
         if(screen.contains(".") && screen.length() > 11) screen = screen.substring(0, 10);
+        if(screen.equals("-0")) screen= "0";
+
     }
+
 }
diff --git a/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java b/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
index ddff0daf..2eb0b519 100644
--- a/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -4,7 +4,7 @@
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
-
+//Kardeena Kameran
 @DisplayName("Retro calculator")
 class CalculatorTest {
 
@@ -90,5 +90,51 @@ void testMultipleDecimalDots() {
 
 
     //TODO hier weitere Tests erstellen
-}
+    @Test
+    @DisplayName("Zeigt das Ergebnis einer Zahl die von einer anderen subtrahiert wird.")
+    void testMinus() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(1);
+        calc.pressDigitKey(0);
+        calc.pressBinaryOperationKey("-");
+        calc.pressDigitKey(5);
+        calc.pressEqualsKey();
+
+        String expected = "5";
+        String actual = calc.readScreen();
 
+        assertEquals(expected, actual);
+    }
+    @Test
+    @DisplayName("Zeigt statt einer -0 immer eine 0 an")
+    void testNegativNull() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(0);
+        calc.pressNegativeKey();
+        calc.pressBinaryOperationKey("+");
+        calc.pressDigitKey(0);
+        calc.pressNegativeKey();
+        calc.pressEqualsKey();
+
+        String expected = "0";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+    @Test
+    @DisplayName("die eingegebene zahl soll nach dem Gleichzeichen wiedergegeben werden")
+    void dreiGleich() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(3);
+        calc.pressEqualsKey();
+
+        String expected = "3";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+}