StructBot is a library for defining function based factories. It excels for use cases involving test cases where you would often define the same struct multiple times (specifically in table driven tests) or where you already have a struct initialized but need to modify a small handful of fields.
go get github.com/tjpnz/structbot
Factories are defined as functions returning a struct and error. They're registered to StructBot using RegisterFactory:
type MyStruct struct {
Foo string
Bar string
}
sb := structbot.New()
sb.RegisterFactory("MyFactory", func() (interface{}, error) {
return &MyStruct{
Foo: "Foo",
Bar: "Bar",
}, nil
})RegisterFactory returns an instance of StructBot which allows multiple factories to be registered at once using chaining.
Factory returns a previously defined factory which can be invoked using Create, Patch, MustCreate or MustPatch - the latter two take a testing.T where errors are passed to Fatalf which is especially useful for testing.
const baseCustomer = "BaseCustomer"
var sb *structbot.StructBot
func init() {
sb = structbot.New()
sb.RegisterFactory(baseCustomer, func() (interface{}, error) {
return &Customer{
FamilyName: "Cleese",
FirstName: "John",
Birthday: time.Date(1939, 10, 27, 0, 0, 0, 0, time.UTC),
Address: &Address{}
}, nil
})
}
func Test_Create(t *testing.T) {
for name, tc := range map[string]struct{
in *Customer
out error
}{
"Valid": {
in: sb.Factory(baseCustomer).MustCreate(t),
}
"ValidationError_Birthday": {
in: sb.Factory(baseCustomer).MustPatch(t, &Customer{
Birthday: time.Date(2100, 1, 1, 0, 0, 0, 0, time.UTC),
}),
out: ErrDateInFuture,
},
"ValidationError_City": {
in: sb.Factory(baseCustomer).MustPatch(t, &Customer{
Address: &Address{
City: "Palmerston North",
}
}),
out: ErrInvalidCity,
},
} {
t.Run(name, func(t *testing.T) {
// Test code
})
}
}StructBot uses Mergo under the hood for patching with overrides enabled. Patching works with nested structs of arbitrary depth. Structs passed to Patch or MustPatch won't overwrite the value on the destination for fields where the source has a zero value. See the Mergo docs for more.