Add unit tests to Income and Expense classes

src/test/java/no/ntnu/idatt1002/demo/data/ExpenseTest.java

+package no.ntnu.idatt1002.demo.data;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ExpenseTest {
+
+    @Test
+    @DisplayName("The Expense constructor throws exceptions when it should.")
+    void constructorThrows(){
+        assertThrows(IllegalArgumentException.class, () -> new Expense("description", 8.5f, false, null));
+        assertThrows(IllegalArgumentException.class, () -> new Expense("description", -10.0f, false, ExpenseCategory.BOOKS));
+    };
+
+    @Test
+    @DisplayName("The Expense constructor does not throw exceptions when it should not.")
+    void constructorDoesThrow() {
+        assertDoesNotThrow(() -> new Expense("description", 59.9f, false,  ExpenseCategory.BOOKS));
+    }
+
+}
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src/test/java/no/ntnu/idatt1002/demo/data/IncomeTest.java

+package no.ntnu.idatt1002.demo.data;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class IncomeTest {
+
+    @Test
+    @DisplayName("The Income constructor throws exceptions when it should.")
+    void constructorThrows(){
+        assertThrows(IllegalArgumentException.class, () -> new Income("description", 8.5f, false, null));
+        assertThrows(IllegalArgumentException.class, () -> new Income("description", -10.0f, false, IncomeCategory.SALARY));
+    };
+
+    @Test
+    @DisplayName("The Income constructor does not throw exceptions when it should not.")
+    void constructorDoesThrow() {
+        assertDoesNotThrow(() -> new Income("description", 59.9f, false, IncomeCategory.SALARY));
+    }
+
+
+}
\ No newline at end of file

src/test/java/no/ntnu/idatt1002/demo/data/ItemTest.java

@@ -10,8 +10,8 @@ class ItemTest {
     @Test
     @DisplayName("The Item constructor throws exceptions when it should.")
     void constructorThrows(){
-        assertThrows(IllegalArgumentException.class, () -> new Item("description", 89.9f, true));
         assertThrows(IllegalArgumentException.class, () -> new Item("description", 0f, false));
+        assertThrows(IllegalArgumentException.class, () -> new Item("description", -10.0f, false));
     };
 
     @Test