Correct some small logical errors in the unit tests of the Ingredient class

src/main/java/no/ntnu/idatt1002/demo/data/recipes/Ingredient.java

@@ -63,7 +63,7 @@ public class Ingredient {
      * @param amount The amount of an ingredient as double.
      */
     public void setAmount(double amount) {
-        if(amount < 0.0f) {
+        if(amount <= 0.0f) {
             throw new IllegalArgumentException("The amount of an ingredient cannot be zero or negative.");
         }
         this.amount = amount;

src/test/java/no/ntnu/idatt1002/demo/data/recipes/IngredientTest.java

@@ -48,7 +48,7 @@ class IngredientTest {
     @DisplayName("Change of food amount works for valid amount.")
     void setAmountWorksForValidAmount() {
         testIngredient.setAmount(2.5);
-        assertEquals(new Ingredient(FoodItem.LEMON, 2.5f, MeasuringUnit.KG), testIngredient);
+        assertEquals(new Ingredient(FoodItem.ONION, 2.5f, MeasuringUnit.KG), testIngredient);
     }
 
     @Test
@@ -62,7 +62,7 @@ class IngredientTest {
     @DisplayName("Change of measuring unit works for valid unit.")
     void setUnitWorksForValidUnit() {
         testIngredient.setUnit(MeasuringUnit.TBS);
-        assertEquals(new Ingredient(FoodItem.LEMON, 0.5f, MeasuringUnit.TBS), testIngredient);
+        assertEquals(new Ingredient(FoodItem.ONION, 0.5f, MeasuringUnit.TBS), testIngredient);
     }
 
     @Test