diff --git a/src/main/java/tdd/setup/Calculator.java b/src/main/java/tdd/setup/Calculator.java
index 171f6d6..f0c12b7 100644
--- a/src/main/java/tdd/setup/Calculator.java
+++ b/src/main/java/tdd/setup/Calculator.java
@@ -34,11 +34,11 @@ public void pressOperationKey(String operation)  {
     }
 
     public void pressDotKey() {
-        if(!screen.endsWith(".")) screen = screen + ".";
+        if (!screen.contains(".")) screen = screen + ".";
     }
 
     public void pressNegative() {
-        screen = screen.startsWith("-") ? screen.substring(1) : "-" + screen;
+        if (!screen.startsWith("-")) screen = "-" + screen;
     }
 
     public void pressEquals() {
diff --git a/src/test/java/tdd/setup/CalculatorTest.java b/src/test/java/tdd/setup/CalculatorTest.java
index 3bf16e9..af0c9c3 100644
--- a/src/test/java/tdd/setup/CalculatorTest.java
+++ b/src/test/java/tdd/setup/CalculatorTest.java
@@ -16,4 +16,44 @@ void calculatorCanDoTwoPlusTwo() {
         calc.pressEquals();
         assertEquals("4", calc.readScreen());
     }
+
+    @Test
+    @DisplayName("Test: should display result after multiplying two positive numbers")
+    void calculatorCanMultiplicate() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(3);
+        calc.pressOperationKey("x");
+        calc.pressDigitKey(4);
+        calc.pressEquals();
+        assertEquals("12", calc.readScreen());
+    }
+
+    @Test
+    @DisplayName("Test: should display result after double using pressNegative")
+    void calculatorUsesMinusCorrectly() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(5);
+        calc.pressNegative();
+        calc.pressNegative();
+        calc.pressOperationKey("x");
+        calc.pressDigitKey(4);
+        calc.pressNegative();
+        calc.pressEquals();
+        assertEquals("20", calc.readScreen());
+
+    }
+
+    @Test
+    @DisplayName("Test: should display result after double using pressDotKey")
+    void calculatorCanClearContents() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(3);
+        calc.pressDotKey();
+        calc.pressDigitKey(5);
+        calc.pressDotKey();
+        calc.pressOperationKey("x");
+        calc.pressDigitKey(4);
+        calc.pressEquals();
+        assertEquals("14", calc.readScreen());
+    }
 }