Correct a Typo and added substract function to the ComplexNumber Object

src/main/java/com/ugsbo/complexnumcalc/ComplexNumber.java

@@ -74,4 +74,21 @@ public class ComplexNumber {
         return sum;
     }
 
+    /**
+     * Substracts the Subtrahend form this instance.
+     * 
+     * @param subtrahend The Number wich will be substracted form the Minuend
+     * @return The Differenz of the Minuend and Subtrahend.
+     */
+    public ComplexNumber substract(ComplexNumber subtrahend) {
+        Double differenzRealPart, differenzImaginaryPart;
+
+        differenzRealPart = this.realPart - subtrahend.realPart;
+        differenzImaginaryPart = this.imaginaryPart - subtrahend.imaginaryPart;
+
+        ComplexNumber differenz = new ComplexNumber(differenzRealPart, differenzImaginaryPart);
+
+        return differenz;
+    }
+
 }

src/test/java/com/ugsbo/complexnumcalc/AddComplexNumbersTest.java

@@ -9,10 +9,10 @@ public class AddComplexNumbersTest {
     @Test
     public void addingTwoComplexNumbersWithoutImaginaryPart() {
         ComplexNumber firstAddend = new ComplexNumber(Double.valueOf(5), Double.valueOf(0));
-        ComplexNumber SecoundAddend = new ComplexNumber(Double.valueOf(6), Double.valueOf(0));
+        ComplexNumber secoundAddend = new ComplexNumber(Double.valueOf(6), Double.valueOf(0));
         ComplexNumber expected = new ComplexNumber(Double.valueOf(11), Double.valueOf(0));
 
-        ComplexNumber sum = firstAddend.add(SecoundAddend);
+        ComplexNumber sum = firstAddend.add(secoundAddend);
 
         assertTrue("Dont sum to the sum", sum.equals(expected));
     }
@@ -20,10 +20,10 @@ public class AddComplexNumbersTest {
     @Test
     public void addingTwoComplexNumbersWithImaginaryPart() {
         ComplexNumber firstAddend = new ComplexNumber(Double.valueOf(5), Double.valueOf(3));
-        ComplexNumber SecoundAddend = new ComplexNumber(Double.valueOf(6), Double.valueOf(4));
+        ComplexNumber secoundAddend = new ComplexNumber(Double.valueOf(6), Double.valueOf(4));
         ComplexNumber expected = new ComplexNumber(Double.valueOf(11), Double.valueOf(7));
 
-        ComplexNumber sum = firstAddend.add(SecoundAddend);
+        ComplexNumber sum = firstAddend.add(secoundAddend);
 
         assertTrue("Dont sum to the sum", sum.equals(expected));
     }

src/test/java/com/ugsbo/complexnumcalc/SubstractComplexNumbersTest.java

@@ -0,0 +1,30 @@
+package com.ugsbo.complexnumcalc;
+
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class SubstractComplexNumbersTest {
+
+    @Test
+    public void substractTwoComplexNumbersWithoutImaginaryPart() {
+        ComplexNumber minuend = new ComplexNumber(Double.valueOf(5), Double.valueOf(0));
+        ComplexNumber subtrahend = new ComplexNumber(Double.valueOf(6), Double.valueOf(0));
+        ComplexNumber expected = new ComplexNumber(Double.valueOf(-1), Double.valueOf(0));
+
+        ComplexNumber difference = minuend.substract(subtrahend);
+
+        assertTrue("The difference is not as expected", difference.equals(expected));
+    }
+
+    @Test
+    public void substractTwoComplexNumbersWithImaginaryPart() {
+        ComplexNumber minuend = new ComplexNumber(Double.valueOf(5), Double.valueOf(5));
+        ComplexNumber subtrahend = new ComplexNumber(Double.valueOf(6), Double.valueOf(4));
+        ComplexNumber expected = new ComplexNumber(Double.valueOf(-1), Double.valueOf(1));
+
+        ComplexNumber difference = minuend.substract(subtrahend);
+
+        assertTrue("The difference is not as expected", difference.equals(expected));
+    }
+}