diff --git a/README.md b/README.md
index ca0f7ebb..6fbb5b5f 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-# Hausaufgabe 1
+    # Hausaufgabe 1
 
 Deadline für Abgabe per Pull Request: 24.10.2021 23:59 Uhr bzw. 27.10.2021 23:59 Uhr je nach dem in welcher Übungsgruppe Sie eingeschrieben sind.
 
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..1e8dcb32 100644
--- a/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -82,7 +82,9 @@ public void pressUnaryOperationKey(String operation) {
         };
         screen = Double.toString(result);
         if(screen.contains(".") && screen.length() > 11) screen = screen.substring(0, 10);
-
+        if(screen.contains("Infinity")) {
+            screen = "Error";
+        }
     }
 
     /**
@@ -122,10 +124,15 @@ public void pressEqualsKey() {
             case "-" -> latestValue - Double.parseDouble(screen);
             case "x" -> latestValue * Double.parseDouble(screen);
             case "/" -> latestValue / Double.parseDouble(screen);
+            case "" -> Double.parseDouble(screen);
             default -> throw new IllegalArgumentException();
         };
         screen = Double.toString(result);
         if(screen.endsWith(".0")) screen = screen.substring(0,screen.length()-2);
         if(screen.contains(".") && screen.length() > 11) screen = screen.substring(0, 10);
+        if(screen.contains("Infinity")) {
+            screen = "Error";
+        }
     }
+
 }
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..75cc11ca 100644
--- a/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -40,6 +40,62 @@ void testSquareRoot() {
         assertEquals(expected, actual);
     }
 
-    //TODO hier weitere Tests erstellen
-}
+    @Test
+    @DisplayName("should clear the screen and set into the default value (0)")
+    void testClearKey() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(5);
+        calc.pressClearKey();
+
+        String expected = "0";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    @DisplayName("should display Error after dividing number 1 with 0")
+    void testDivisionWithZero() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(7);
+        calc.pressBinaryOperationKey("/");
+        calc.pressDigitKey(0);
+        calc.pressEqualsKey();
+
+        String expected = "Error";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
 
+    @Test
+    @DisplayName("should display Error after press inversion without press digit key")
+    void testPressInversionKey() {
+        Calculator calc = new Calculator();
+
+        calc.pressUnaryOperationKey("1/x");
+
+        String expected = "Error";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    @DisplayName("should display decimal numbers on screen like 4.5 after pressing Equalskey")
+    void testPressDotkeyAndPressEqualskey() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(4);
+        calc.pressDotKey();
+        calc.pressDigitKey(5);
+        calc.pressEqualsKey();
+
+        String expected = "4.5";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+}
\ No newline at end of file