SetAsserter works only outside unit tests, they MUST use pkg asserter

assert/assert.go

@@ -967,8 +967,6 @@ func doNotZero[T Number](val T, a []any) {
 //
 // NOTE that since our TLS [asserterMap] we still continue to use indexing.
 func current() (curAsserter asserter) {
-	// we need thread local storage, maybe we'll implement that to x.package?
-	// study `tester` and copy ideas from it.
 	tlsID := goid()
 	asserterMap.Rx(func(m map[int]asserter) {
 		aster, found := m[tlsID]
@@ -1023,9 +1021,16 @@ func SetDefault(i defInd) (old defInd) {
 // to return plain error messages instead of the panic asserts, they can use
 // following:
 //
-//	assert.SetAsserter(assert.Plain)
+//	defer assert.SetAsserter(assert.Plain)()
 func SetAsserter(i defInd) func() {
-	asserterMap.Set(goid(), defAsserter[i])
+	// get pkg lvl asserter
+	curAsserter := defAsserter[def]
+	// ..  to check if we are doing unit tests
+	if !curAsserter.isUnitTesting() {
+		// .. allow TLS specific asserter. NOTE see current()
+		curGoRID := goid()
+		asserterMap.Set(curGoRID, defAsserter[i])
+	}
 	return popCurrentAsserter
 }
 

assert/assert_test.go

@@ -261,6 +261,22 @@ func ExampleCLen() {
 	// Output: sample: assert_test.go:253: ExampleCLen.func1(): assertion failure: length: got '2', want '3'
 }
 
+func ExampleThatNot() {
+	sample := func() (err error) {
+		defer err2.Handle(&err)
+
+		assert.ThatNot(true, "overrides if Plain asserter")
+		return err
+	}
+
+	// set asserter for this thread/goroutine only, we want plain errors
+	defer assert.SetAsserter(assert.Plain)()
+
+	err := sample()
+	fmt.Printf("%v", err)
+	// Output: testing: run example: overrides if Plain asserter
+}
+
 func BenchmarkMKeyExists(b *testing.B) {
 	bs := map[int]int{0: 0, 1: 1}
 	for n := 0; n < b.N; n++ {