From b1a2ba85726f4d124bf349bb649d19dbb2f3638f Mon Sep 17 00:00:00 2001
From: kyeorai <kiet-dinh@gmx.de>
Date: Mon, 27 Apr 2026 23:39:37 +0200
Subject: [PATCH] Add tests and fix calculator bugs

---
 .../java/htw/berlin/prog2/ha1/Calculator.java |  1 +
 .../htw/berlin/prog2/ha1/CalculatorTest.java  | 36 ++++++++++++++++++-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/src/main/java/htw/berlin/prog2/ha1/Calculator.java b/src/main/java/htw/berlin/prog2/ha1/Calculator.java
index 84c04f2..538f796 100644
--- a/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -118,6 +118,7 @@ public void pressNegativeKey() {
      * und das Ergebnis direkt angezeigt.
      */
     public void pressEqualsKey() {
+        if(latestOperation.equals("")) return;
         var result = switch(latestOperation) {
             case "+" -> latestValue + Double.parseDouble(screen);
             case "-" -> latestValue - Double.parseDouble(screen);
diff --git a/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java b/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
index ddff0da..b64378b 100644
--- a/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -90,5 +90,39 @@ void testMultipleDecimalDots() {
 
 
     //TODO hier weitere Tests erstellen
-}
 
+    @Test
+    @DisplayName("should multiply two numbers")
+    void testMultiplication() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(3);
+        calc.pressBinaryOperationKey("x");
+        calc.pressDigitKey(4);
+        calc.pressEqualsKey();
+
+        assertEquals("12", calc.readScreen());
+
+    }
+    @Test
+    @DisplayName("should not change value when equals pressed without operation")
+    void testEqualsWithoutOperation() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(5);
+        calc.pressEqualsKey();
+
+        assertEquals("5", calc.readScreen());
+    }
+    @Test
+    @DisplayName("should toggle negative sign correctly")
+    void testNegativeToggle() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(7);
+        calc.pressNegativeKey();
+        calc.pressNegativeKey();
+
+        assertEquals("7", calc.readScreen());
+    }
+}
\ No newline at end of file