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..1bf80dd9 100644
--- a/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -45,9 +45,15 @@ public void pressDigitKey(int digit) {
      * im Ursprungszustand ist.
      */
     public void pressClearKey() {
-        screen = "0";
-        latestOperation = "";
-        latestValue = 0.0;
+        if(!screen.equals("0")){
+            screen = "0";
+        } else {
+            screen = "0";
+            latestOperation = "";
+            latestValue = 0.0;
+        }
+
+        //C taste fehlt bei wiederholtem drücken CE
     }
 
     /**
@@ -105,7 +111,11 @@ public void pressDotKey() {
      * entfernt und der Inhalt fortan als positiv interpretiert.
      */
     public void pressNegativeKey() {
-        screen = screen.startsWith("-") ? screen.substring(1) : "-" + screen;
+        if (screen.equals("0") || screen.equals(-0)) {
+            screen = "0";
+        } else{
+            screen = screen.startsWith("-") ? screen.substring(1) : "-" + screen;
+    }
     }
 
     /**
@@ -130,4 +140,13 @@ public void pressEqualsKey() {
         if(screen.endsWith(".0")) screen = screen.substring(0,screen.length()-2);
         if(screen.contains(".") && screen.length() > 11) screen = screen.substring(0, 10);
     }
-}
+/*
+    public static void main(String[]args){
+        double a = 7;
+        double b = 9;
+
+        System.out.println(b / a);
+ */
+
+    }
+
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..f4161961 100644
--- a/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -88,7 +88,93 @@ void testMultipleDecimalDots() {
         assertEquals(expected, actual);
     }
 
-
     //TODO hier weitere Tests erstellen
+
+    @Test
+    @DisplayName("should display positive result after division of two positive numbers")
+    void testPositiveDivision(){
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(1);
+        calc.pressDigitKey(0);
+        calc.pressBinaryOperationKey("/");
+        calc.pressDigitKey(5);
+        calc.pressEqualsKey();
+
+        String expected = "2";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    @DisplayName("should display at most 10 characters on screen")
+    void testScreenLengthLimit(){
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(9);
+        calc.pressBinaryOperationKey("/");
+        calc.pressDigitKey(7);
+        calc.pressEqualsKey();
+
+        String expected = "1.28571428";
+        String actual = calc.readScreen();
+
+        System.out.println(actual);
+        System.out.println(actual.length());
+
+        assertEquals(true, actual.length()<= 10);
+    }
+
+    @Test
+    @DisplayName("should only clear screen on first press of C and full reeset on second")
+    void testClearKey(){
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(2);
+        calc.pressBinaryOperationKey("+");
+        calc.pressDigitKey(5);
+        calc.pressClearKey();
+        calc.pressEqualsKey();
+
+        String expected = "2";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+
+    }
+
+    @Test
+    @DisplayName("should not allow two points in one number")
+
+    void testDoubleDot(){
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(5);
+        calc.pressDotKey();
+        calc.pressDigitKey(6);
+        calc.pressDotKey();
+        calc.pressDigitKey(7);
+
+        String expected = "5.67";
+        String actual = calc.readScreen();
+
+        assertEquals(expected,actual);
+    }
+
+    @Test
+    @DisplayName("should not write a negative sign before 0")
+    void testNegativeKeyOnZero(){
+        Calculator calc = new Calculator();
+
+        calc.pressNegativeKey();
+
+        String expected = "0";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
 }
 
+