test: add SliceNotContainsFunc assertion (#115)

Fixes: #110

internal/assertions/assertions.go

@@ -406,6 +406,14 @@ func SliceNotContains[A any](slice []A, item A, opts ...cmp.Option) (s string) {
 	return
 }
 
+func SliceNotContainsFunc[A, B any](slice []A, item B, eq func(a A, b B) bool) (s string) {
+	if containsFunc(slice, item, eq) {
+		s = "expected slice to not contain item but it does\n"
+		s += bullet("unwanted item %#v\n", item)
+	}
+	return
+}
+
 func SliceContainsAll[A any](slice, items []A) (s string) {
 	if len(slice) != len(items) {
 		s = "expected slice and items to contain same number of elements\n"

test.go

@@ -216,6 +216,13 @@ func SliceNotContains[A any](t T, slice []A, item A, settings ...Setting) {
 	invoke(t, assertions.SliceNotContains(slice, item), settings...)
 }
 
+// SliceNotContainsFunc asserts item does not exist inslice, using eq to compare
+// elements.
+func SliceNotContainsFunc[A, B any](t T, slice []A, item B, eq func(a A, b B) bool, settings ...Setting) {
+	t.Helper()
+	invoke(t, assertions.SliceNotContainsFunc(slice, item, eq), settings...)
+}
+
 // SliceContainsAll asserts slice and items contain the same elements, but in
 // no particular order. The number of elements in slice and items must be the
 // same.

test_test.go

@@ -649,6 +649,23 @@ func TestSliceNotContains(t *testing.T) {
 	SliceNotContains(tc, s, &Person{ID: 101, Name: "Bob"})
 }
 
+func TestSliceNotContainsFunc(t *testing.T) {
+	tc := newCase(t, `expected slice to not contain item but it does`)
+	t.Cleanup(tc.assert)
+
+	s := []*Person{
+		{ID: 100, Name: "Alice"},
+		{ID: 101, Name: "Bob"},
+		{ID: 102, Name: "Carla"},
+	}
+
+	f := func(a, b *Person) bool {
+		return a.Name == b.Name && a.ID == b.ID
+	}
+
+	SliceNotContainsFunc(tc, s, &Person{ID: 101, Name: "Bob"}, f)
+}
+
 func TestSliceContainsAll(t *testing.T) {
 	t.Run("wrong element", func(t *testing.T) {
 		tc := newCase(t, `expected slice to contain missing item`)