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 aaef8862..e1aef384 100644
--- a/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -30,8 +30,8 @@ public String readScreen() {
      */
     public void pressDigitKey(int digit) {
         if(digit > 9 || digit < 0) throw new IllegalArgumentException();
-
-        if(screen.equals("0") || latestValue == Double.parseDouble(screen)) screen = "";
+        if(screen.equals("-0")) screen = "-";
+        else if(screen.equals("0") || latestValue == Double.parseDouble(screen)) screen = "";
 
         screen = screen + digit;
     }
@@ -125,6 +125,9 @@ public void pressEqualsKey() {
             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);
     }
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 addc5f26..5bbf0ecc 100644
--- a/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -41,5 +41,50 @@ void testSquareRoot() {
     }
 
     //TODO hier weitere Tests erstellen
+    @Test
+    @DisplayName("should display result after multiplying two positive digit numbers")
+    void testPositivMultiplikation() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(1);
+        calc.pressDigitKey(2);
+        calc.pressBinaryOperationKey("x");
+        calc.pressDigitKey(3);
+        calc.pressEqualsKey();
+
+        String expected = "36";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+    @Test
+    @DisplayName("should display result after dividing one positive multi-digit number with zero")
+    void testDivideZero() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(1);
+        calc.pressDigitKey(0);
+        calc.pressBinaryOperationKey("/");
+        calc.pressDigitKey(0);
+        calc.pressEqualsKey();
+
+        String expected = "Error";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+    @Test
+    @DisplayName("should display result of pressing negative key before pressing digit key")
+    void testNegativeKey() {
+        Calculator calc = new Calculator();
+
+        calc.pressNegativeKey();
+        calc.pressDigitKey(3);
+
+        String expected = "-3";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
 }