examples: make examples testable

examples/o2obidi/README.md

@@ -9,3 +9,9 @@ B can get its spouse using the `spouse` edge.
 ```console
 go generate ./...
 ```
+
+### Run Examples
+
+```console
+go test
+```

examples/o2obidi/example_test.go

@@ -15,20 +15,25 @@ import (
 	_ "github.com/mattn/go-sqlite3"
 )
 
-func main() {
+func Example_O2OBidi() {
 	client, err := ent.Open("sqlite3", "file:ent?mode=memory&cache=shared&_fk=1")
 	if err != nil {
 		log.Fatalf("failed opening connection to sqlite: %v", err)
 	}
 	defer client.Close()
 	ctx := context.Background()
-	// run the auto migration tool.
+	// Run the auto migration tool.
 	if err := client.Schema.Create(ctx); err != nil {
 		log.Fatalf("failed creating schema resources: %v", err)
 	}
 	if err := Do(ctx, client); err != nil {
 		log.Fatal(err)
 	}
+	// Output:
+	// a8m
+	// nati
+	// 2
+	// nati
 }
 
 func Do(ctx context.Context, client *ent.Client) error {