Ensure set.Equal() compares the two set lengths

set.Equal() currently checks the length of the owning set against
itself, so a.Equal(b) returns true if a is a superset of b, with no
further restriction.

This fixes the length check and adds unit tests to catch this case.

Signed-off-by: Stephen Kitt <skitt@redhat.com>

set/set.go

@@ -155,7 +155,7 @@ func (s Set[E]) Difference(s2 Set[E]) Set[E] {
 // Equal returns true if and only if s1 is equal (as a set) to s2.
 // Two sets are equal if their membership is identical.
 func (s Set[E]) Equal(s2 Set[E]) bool {
-	return s.Len() == s.Len() && s.IsSuperset(s2)
+	return s.Len() == s2.Len() && s.IsSuperset(s2)
 }
 
 type sortableSlice[E ordered] []E

set/set_test.go

@@ -169,11 +169,17 @@ func TestStringSetEquals(t *testing.T) {
 	if a.Equal(b) {
 		t.Errorf("Expected to be not-equal: %v vs %v", a, b)
 	}
+	if b.Equal(a) {
+		t.Errorf("Expected to be not-equal: %v vs %v", b, a)
+	}
 
 	b = New[string]("1", "2", "")
 	if a.Equal(b) {
 		t.Errorf("Expected to be not-equal: %v vs %v", a, b)
 	}
+	if b.Equal(a) {
+		t.Errorf("Expected to be not-equal: %v vs %v", b, a)
+	}
 
 	// Check for equality after mutation
 	a = New[string]()