BUGFIX: Disallow updating course capacity if the value is not new

src/Model/Aggregate/CourseCapacityAggregate.php

@@ -48,6 +48,9 @@ public function apply(DomainEvent $domainEvent): void
 
     public function changeCourseCapacity(CourseCapacity $newCapacity): void
     {
+        if ($newCapacity->equals($this->state->courseCapacity)) {
+            throw new ConstraintException(sprintf('Failed to change capacity of course with id "%s" to %d because that is already the courses capacity', $this->courseId->value, $newCapacity->value), 1686819073);
+        }
         if ($this->state->numberOfSubscriptions > $newCapacity->value) {
             throw new ConstraintException(sprintf('Failed to change capacity of course with id "%s" to %d because it already has %d active subscriptions', $this->courseId->value, $newCapacity->value, $this->state->numberOfSubscriptions), 1684604361);
         }

src/Model/CourseCapacity.php

@@ -22,6 +22,11 @@ public static function fromInteger(int $value): self
         return new self($value);
     }
 
+    public function equals(self $other): bool
+    {
+        return $other->value === $this->value;
+    }
+
     public function jsonSerialize(): int
     {
         return $this->value;

tests/Behat/CourseConstraints.feature

@@ -22,6 +22,14 @@ Feature:
       Failed to change capacity of course with id "non-existing" to 3 because a course with that id does not exist
       """
 
+  Scenario:
+    Given course "c1" exists with a capacity of 3
+    When course "c1" capacity is changed to 3
+    Then the command should be rejected with the following message:
+      """
+      Failed to change capacity of course with id "c1" to 3 because that is already the courses capacity
+      """
+
   Scenario:
     Given course "c1" exists with the title "Some Course Title"
     When course "c1" is renamed to "Some Course Title"