Go does not recognize a func as a valid interface - go

I have the func
func(context.Context, *domain.Scorecard) (*domain.Scorecard, error)
And i want pass this as a param that receive a interface
warehouse interface {
Get(context.Context, *domain.Scorecard) (*domain.Scorecard, error)
}
Ex:
warehouseMock :=
usecase.WithScenarioFinder(
func(player *domain.Player) (*domain.Scenario, error) {
return nil,nil
)
The traditional form is create a struct that have the method Get, but i have curiosity if exist the way to tell "hey, that is a simple func, is the same firm (with no name), accept it"


Functions do not implement interfaces with only a single method of that same signature. See this Go issue for a discussion on the topic.
Create an adaptor type to convert a function to an interface:
type WarehouseFunc func(context.Context, *domain.Scorecard) (*domain.Scorecard, error)
func (f WarehouseFunc) Get(c context.Context, d *domain.Scorecard) (*domain.Scorecard, error) {
return f(c, d)
}
Convert an anonymous function to an interface like this:
itf = WarehouseFunc(func(c context.Context, d *domain.Scorecard) (*domain.Scorecard, error) {
return nil, nil
})

Related

Mocking via stretchr/testify, different return args

Function below describes how to mock using testify. args.Bool(0), args.Error(1) are mocked positional return values.
func (m *MyMockedObject) DoSomething(number int) (bool, error) {
args := m.Called(number)
return args.Bool(0), args.Error(1)
}
Is it possible to return anything other than args.Int(), args.Bool(), args.String()? What if I need to return int64, or a custom struct. Is there a method or am I missing something?
For example:
func (m *someMock) doStuff(p *sql.DB, id int) (res int64, err error)

Yes, it is possible by using args.Get and type assertion.
From the docs:
// For objects of your own type, use the generic Arguments.Get(index) method and make a type assertion:
//
// return args.Get(0).(*MyObject), args.Get(1).(*AnotherObjectOfMine)
So, your example would be:
func (m *someMock) doStuff(p *sql.DB, id int) (res int64, err error) {
args := m.Called(p, id)
return args.Get(0).(int64), args.Error(1)
}
Additionaly, if your return value is a pointer (e.g. pointer to struct), you should check if it is nil before performing type assertion.

Calling the same function on two different structs

I've got two functions that accept different pointers pointing to different structs, but the structs have the same underlying function.
func Save(db *sql.DB) error {
db.Prepare(query)
}
func TxSave(tx *sql.Tx) error {
tx.Prepare(query)
}
I don't want to have to make changes in both functions when I need to extend this function in the future. How do I adhere to DRYness in golang with this scenario?

Create an interface such as:
type SQLRunner interface{
Prepare(query string) (*sql.Stmt, error)
PrepareContext(ctx context.Context, query string) (*sql.Stmt, error)
Query(query string, args ...interface{}) (*Rows, error)
QueryContext(ctx context.Context, query string, args ...interface{}) (*sql.Rows, error)
// add as many method shared by both sql.Tx qnd sql.DB
// ...
}
And then create a single method taking that interface:
func Save(s SQLRunner) error {
s.Prepare()
}
In go interface implementation is implicit, so you just have to pass *sql.Tx or *sql.DB to the save function:
Save(tx)
Save(db)
Here a good blog post about interfaces in go:http://jordanorelli.com/post/32665860244/how-to-use-interfaces-in-go

Wow, I think I'm in love with Go. I can actually just do this by creating my own interface.
type Saver interface {
Prepare(query string) (*sql.Stmt, error)
}
func Save(db *sql.DB) error {
return GenericSave(db)
}
func TxSave(tx *sql.Tx) error {
return GenericSave(tx)
}
func GenericSave(saver Saver) error {
stmt := saver.Prepare(query)
// Do rest with saver
}

How do you mock a type within a type in Golang?

The package 'gopkg.in/redis.v3' contains some code
type Client struct {
}
func (*client) Eval (string, []string, []string) *Cmd {
}
type Cmd struct {
}
func (*Cmd) Result () (interface{}, error) {
}
Which works successfully in the following way
func myFunc (cli *redis.Client) {
result, err := cli.Eval('my script').Result()
}
The problem is that sometimes the Redis cluster gets hammered, has a moment, and the interface returned as a result is nil.
This is reasonably easy to handle but I wish to put a test in place that will ensure that it is actually handled and no type assertion panic occurs.
Traditionally I would insert a mock Redis client into myFunc that can ultimately return nil.
type redisClient interface {
Eval(string, []string, []string) redisCmd
}
type redisCmd interface {
Result() (interface{}, error)
}
func myFunc (cli redisClient) {
result, err := cli.Eval('my script').Result()
}
The problem I am facing is the compiler doesn't recognise that redis.Client satisfies the interface redisClient because it doesn't recognise that the redis.Cmd returned from Eval satisfies redisCmd.
> cannot use client (type *redis.Client) as type redisClient in argument to myFunc:
> *redis.Client does not implement redisClient (wrong type for Eval method)
> have Eval(sting, []string, []string) *redis.Cmd
> want Eval(sting, []string, []string) redisCmd

The problem is that your interface does not match the redis client. If you change the interface to:
type redisClient interface {
Eval(string, []string, []string) *redis.Cmd
}
it will compile. That being said, it looks like you really want rediscmd, so you will need to make a wrapper around the redis client:
type wrapper struct{
c *redis.Client
}
func (w wrapper) Eval(x sting, y []string, z []string) redisCmd {
return w.c.Eval(x,y,z) // This assumes that *redis.Cmd implements rediscmd
}

Mocking a Go database SDK

I am attempting to create a wrapper for test emulating around the Go Flex SDK for Google Cloud Datastore. While I am currently successfully running the localhost emulator using
gcloud beta emulators datastore start --no-store-on-disk
in a separate terminal from my testing window, I would prefer to create a mock database emulator that runs as part of the test process itself (without execing the above) so that I can run multiple tests in parallel, each with its own database emulator.
I have run into a problem with the Google SDK not implementing my interface.
My wrapper contains this code:
package google
import (
"context"
"cloud.google.com/go/datastore"
)
type (
// Datastore is a wrapper for the Google Cloud Datastore Client.
Datastore datastore.Client
// Datastorer represents things that can operate like a datastore.Client.
Datastorer interface {
Delete(context.Context, *datastore.Key) error
Get(context.Context, *datastore.Key, interface{}) error
GetAll(context.Context, *datastore.Query, interface{}) ([]*datastore.Key, error)
Put(context.Context, *datastore.Key, interface{}) (*datastore.Key, error)
PutMulti(context.Context, []*datastore.Key, interface{}) ([]*datastore.Key, error)
RunInTransaction(context.Context, func(Transactioner) error, ...datastore.TransactionOption) (*datastore.Commit, error)
}
// Transactioner represents things that can operate like a datastore.Transaction.
Transactioner interface {
Commit() (*datastore.Commit, error)
Delete(*datastore.Key) error
DeleteMulti([]*datastore.Key) error
Get(*datastore.Key, interface{}) error
GetMulti([]*datastore.Key, interface{}) error
Put(*datastore.Key, interface{}) (*datastore.PendingKey, error)
PutMulti([]*datastore.Key, interface{}) ([]*datastore.PendingKey, error)
Rollback() error
}
)
// Delete deletes the entity for the given key.
func (d *Datastore) Delete(ctx context.Context, key *datastore.Key) error {
return (*datastore.Client)(d).Delete(ctx, key)
}
// Get retrieves the entity for the given key.
func (d *Datastore) Get(ctx context.Context, key *datastore.Key, dst interface{}) error {
return (*datastore.Client)(d).Get(ctx, key, dst)
}
// GetAll retrieves all entities for the given query.
func (d *Datastore) GetAll(ctx context.Context, q *datastore.Query, dst interface{}) ([]*datastore.Key, error) {
return (*datastore.Client)(d).GetAll(ctx, q, dst)
}
// Put stores an entity for the given key.
func (d *Datastore) Put(ctx context.Context, key *datastore.Key, src interface{}) (*datastore.Key, error) {
return (*datastore.Client)(d).Put(ctx, key, src)
}
// PutMulti is a batch version of Put.
func (d *Datastore) PutMulti(ctx context.Context, keys []*datastore.Key, src interface{}) ([]*datastore.Key, error) {
return (*datastore.Client)(d).PutMulti(ctx, keys, src)
}
// RunInTransaction runs the given function in a transaction.
func (d *Datastore) RunInTransaction(ctx context.Context, f func(tx Transactioner) error, opts ...datastore.TransactionOption) (*datastore.Commit, error) {
return (*datastore.Client)(d).RunInTransaction(ctx, func(t *datastore.Transaction) error {
return f(t)
}, opts...)
}
Note that these interfaces do not emulate the complete SDK. I am only including functions that I actually call in my code. I'll add new ones as needed later.
When I try to use an instance of *datastore.Client as a Datastorer, I get the following error:
cannot use client (type *"cloud.google.com/go/datastore".Client) as type Datastorer in field value:
*"cloud.google.com/go/datastore".Client does not implement Datastorer (wrong type for RunInTransaction method)
have RunInTransaction(context.Context, func(*"cloud.google.com/go/datastore".Transaction) error, ..."cloud.google.com/go/datastore".TransactionOption) (*"cloud.google.com/go/datastore".Commit, error)
want RunInTransaction(context.Context, func(Transactioner) error, ..."cloud.google.com/go/datastore".TransactionOption) (*"cloud.google.com/go/datastore".Commit, error)
because *datastore.Client requires a function that takes a func(*datastore.Transaction) error and my interface wants a func(Transactioner) error.
Is there any way to change this so that it compiles?
If I can get it working, I plan to create types that implement my Datastorer and Transactioner interfaces and use maps to mock the real database. As far as tranactions go, for testing I can use sync.Mutex if I need them, but since each test is a single thread and will get its own database object, I may not need to lock them.

I've gotten it to compile by using this code:
package google
import (
"context"
"cloud.google.com/go/datastore"
)
type (
// Datastore is a wrapper for the Google Cloud Datastore Client.
Datastore struct {
*datastore.Client
}
// Datastorer represents things that can operate like a datastore.Client.
Datastorer interface {
Delete(context.Context, *datastore.Key) error
Get(context.Context, *datastore.Key, interface{}) error
GetAll(context.Context, interface{}, interface{}) ([]*datastore.Key, error)
Put(context.Context, *datastore.Key, interface{}) (*datastore.Key, error)
PutMulti(context.Context, []*datastore.Key, interface{}) ([]*datastore.Key, error)
RunInTransaction(context.Context, func(Transactioner) error, ...datastore.TransactionOption) (*datastore.Commit, error)
}
// Querier represents things that can operate like a datastore.Query.
Querier interface {
Filter(string, interface{}) Querier
}
// Transactioner represents things that can operate like a datastore.Transaction.
Transactioner interface {
Commit() (*datastore.Commit, error)
Delete(*datastore.Key) error
DeleteMulti([]*datastore.Key) error
Get(*datastore.Key, interface{}) error
GetMulti([]*datastore.Key, interface{}) error
Put(*datastore.Key, interface{}) (*datastore.PendingKey, error)
PutMulti([]*datastore.Key, interface{}) ([]*datastore.PendingKey, error)
Rollback() error
}
)
// Delete deletes the entity for the given key.
func (d *Datastore) Delete(ctx context.Context, key *datastore.Key) error {
return d.Client.Delete(ctx, key)
}
// Get retrieves the entity for the given key.
func (d *Datastore) Get(ctx context.Context, key *datastore.Key, dst interface{}) error {
return d.Client.Get(ctx, key, dst)
}
// GetAll retrieves all entities for the given query.
func (d *Datastore) GetAll(ctx context.Context, q interface{}, dst interface{}) ([]*datastore.Key, error) {
return d.Client.GetAll(ctx, q.(*datastore.Query), dst)
}
// Put stores an entity for the given key.
func (d *Datastore) Put(ctx context.Context, key *datastore.Key, src interface{}) (*datastore.Key, error) {
return d.Client.Put(ctx, key, src)
}
// PutMulti is a batch version of Put.
func (d *Datastore) PutMulti(ctx context.Context, keys []*datastore.Key, src interface{}) ([]*datastore.Key, error) {
return d.Client.PutMulti(ctx, keys, src)
}
// RunInTransaction runs the given function in a transaction.
func (d *Datastore) RunInTransaction(ctx context.Context, f func(tx Transactioner) error, opts ...datastore.TransactionOption) (*datastore.Commit, error) {
return d.Client.RunInTransaction(ctx, func(t *datastore.Transaction) error {
return f(t)
}, opts...)
}
I changed DataStore to a struct containing the datastore.Client and added a new interface Querier that contains the functions that I am using from datastore.Query. I also updated GetAll to accept an interface{} instead of a *datastore.Query and then type-assert it to be a *datastore.Query. I cannot have it accept a Querier because then I cannot pass variables of type *datastore.Query because they do not satisfy the Querier interface (Filter returns a Querier instead of a *datastore.Query).
All existing tests using the emulator running in a separate process are passing.
UPDATE:
I changed Datastore to
Datastore datastore.Client
and added a wrapper Query around datastore.Query:
Query datastore.Query
Now, the Datastorer interface contains
GetAll(context.Context, Querier, interface{}) ([]*datastore.Key, error)
and the GetAll function is defined as
func (d *Datastore) GetAll(ctx context.Context, q Querier, dst interface{}) ([]*datastore.Key, error) {
return (*datastore.Client)(d).GetAll(ctx, (*datastore.Query)(q.(*Query)), dst)
}
and Query.Filter is defined as
func (q *Query) Filter(filterStr string, value interface{}) Querier {
return (*Query)((*datastore.Query)(q).Filter(filterStr, value))
}
In calling code, I use
q := datastore.NewQuery(entity).Filter("Deleted =", false)
_, err := r.client.GetAll(ctx, (*Query)(q), data)
This compiles and all tests are passing.

I know that question has been asked a long time ago but in case one still may wondering how to Mock Google Datastore Client and Transaction here is a snapshot of how I got it to work.
type Client interface {
Get(ctx context.Context, key *datastore.Key, dst interface{}) (err error)
NewTransaction(ctx context.Context, opts ...datastore.TransactionOption) (t Transaction, err error)
Put(ctx context.Context, key *datastore.Key, src interface{}) (*datastore.Key, error)
}
type Transaction interface {
Commit() (c *datastore.Commit, err error)
Rollback() (err error)
Get(key *datastore.Key, dst interface{}) (err error)
Put(key *datastore.Key, src interface{}) (*datastore.PendingKey, error)
Delete(key *datastore.Key) error
}
type Datastore struct {
*datastore.Client
}
func (d *Datastore) NewTransaction(ctx context.Context, opts ...datastore.TransactionOption) (t Transaction, err error) {
return d.Client.NewTransaction(ctx, opts...)
}
Of course, If you are using different method against Datastore it's up to you to implement them.
In my tests, I can now Mock Datastore Client and Transaction like :
mockedClient := mock_gcloud.NewMockClient(ctrl)
mockedTransaction := mock_gcloud.NewMockTransaction(ctrl)
...
mockedClient.EXPECT().NewTransaction(context.Background()).Return(mockedTransaction, nil).Times(1)
Et voilà.

For a given interface, I have three implementations. How the three implementation share a same method?

I have an interface:
type Reader interface {
// Read IV and Master header
ReadMaster(p []byte, full bool) (int, error)
// Read User header
ReadUser(p []byte, full bool) (int, error)
// Read Content data
ReadContent(p []byte) (int, error)
}
And I have three structs are compatible with the interface. All the three structs have the samve method ReadUser. So I have to do:
func (r *s1) ReadUser(buf []byte, full bool) (int, error) {
//.... code 1 ....
}
func (r *s2) ReadUser(buf []byte, full bool) (int, error) {
//.... code 2 ....
}
func (r *s3) ReadUser(buf []byte, full bool) (int, error) {
//.... code 3 ....
}
However, the "code1", "code2" and "code3" above are exactly the same. It's there a good way to reduce the duplicate codes? E.g. define the function once and assign it to three struct?

Wrap it in its own type. Remembering too that interfaces in Go should only provide contracts for small specific tasks. It is very common for an interface to contain only a single method.
type UserReader interface {
ReadUser(p []byte, full bool) (int, error)
}
type UserRepo struct {
}
Add the method to that type:
func (ur *UserRepo) ReadUser(p []byte, full bool) (int, error) {
// code to read a user
}
Then, embed it in your other types:
type s1 struct {
*UserRepo
// other stuff here..
}
type s2 struct {
*UserRepo
// other stuff here..
}
type s3 struct {
*UserRepo
// other stuff here..
}
Then you can:
u := s1{}
i, err := u.ReadUser(..., ...)
u2 := s2{}
i2, err2 := u2.ReadUser(..., ...)
// etc..
..and you can also do:
doStuff(u)
doStuff(u2)
.. where doStuff is:
func doStuff(u UserReader) {
// any of the three structs
}
Click here to see it in the Playground

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