diff --git a/internal/set/set.go b/internal/set/set.go
index 5c7bcabef8..3e777fe124 100644
--- a/internal/set/set.go
+++ b/internal/set/set.go
@@ -24,11 +24,11 @@ func NewWithValues[E comparable](values ...E) *Set[E] {
 	return s
 }
 
-func (s Set[E]) Add(v E) {
+func (s *Set[E]) Add(v E) {
 	s.m[v] = struct{}{} // Possibly writing the same struct{}{} presence marker again.
 }
 
-func (s Set[E]) Delete(v E) {
+func (s *Set[E]) Delete(v E) {
 	delete(s.m, v)
 }
 
diff --git a/internal/set/set_test.go b/internal/set/set_test.go
new file mode 100644
index 0000000000..f568730701
--- /dev/null
+++ b/internal/set/set_test.go
@@ -0,0 +1,66 @@
+package set
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNew(t *testing.T) {
+	s := New[int]()
+	assert.True(t, s.Empty())
+}
+
+func TestNewWithValues(t *testing.T) {
+	s := NewWithValues(1, 3)
+	assert.True(t, s.Contains(1))
+	assert.False(t, s.Contains(2))
+	assert.True(t, s.Contains(3))
+}
+
+func TestAdd(t *testing.T) {
+	s := NewWithValues(1)
+	assert.False(t, s.Contains(2))
+	s.Add(2)
+	assert.True(t, s.Contains(2))
+	s.Add(2) // Adding an already-present element
+	assert.True(t, s.Contains(2))
+	// Unrelated elements are unaffected
+	assert.True(t, s.Contains(1))
+	assert.False(t, s.Contains(3))
+}
+
+func TestDelete(t *testing.T) {
+	s := NewWithValues(1, 2)
+	assert.True(t, s.Contains(2))
+	s.Delete(2)
+	assert.False(t, s.Contains(2))
+	s.Delete(2) // Deleting a missing element
+	assert.False(t, s.Contains(2))
+	// Unrelated elements are unaffected
+	assert.True(t, s.Contains(1))
+}
+
+func TestContains(t *testing.T) {
+	s := NewWithValues(1, 2)
+	assert.True(t, s.Contains(1))
+	assert.True(t, s.Contains(2))
+	assert.False(t, s.Contains(3))
+}
+
+func TestEmpty(t *testing.T) {
+	s := New[int]()
+	assert.True(t, s.Empty())
+	s.Add(1)
+	assert.False(t, s.Empty())
+	s.Delete(1)
+	assert.True(t, s.Empty())
+}
+
+func TestValues(t *testing.T) {
+	s := New[int]()
+	assert.Empty(t, s.Values())
+	s.Add(1)
+	s.Add(2)
+	assert.ElementsMatch(t, []int{1, 2}, s.Values())
+}