Use test cases and table testing to fully test cover Exported functions. Stop writing huge tests that can be written in less line thanks to table testing.

Change checks fro empty strings from:

someString := ""

if len(someString) == 0 {
    ...
}

to

someString := ""

if someString == "" {
    ...
}

to have a more idiomatic go.

As above, Similarity field in struct FaceMatches has wrong type int, should be float64 instead

In order to have more idiomatic go, replace all new(T); T.SetFirstname("Bob") with &T{Firstname: "Bob"}. Then, remove unused Set methods.

Remove tests for private functions. We should cover the latters in the different tests of functions that rely on them with suitable test cases (table tests) and proper mocks.

At the moment, errors' context is badly handled. We should wrap errors like:

package user

import (
    "github.com/pkg/errors"
)

var (
    // ErrInvalidParam used when a parameter is invalid
    ErrInvalidParam = errors.New("invalid param")
)
 // User represents a user
type User struct {
    FirstName string
    LastName string
}

func (u *User) validate() error {
    
    if u.FirstName == "" {
        return errors.Wrap(ErrInvalidParam, "param : %s", "FirstName")
    }
    if u.LastName == "" {
        return errors.Wrap(ErrInvalidParam, "param : %s", "LastName")
    }

    return nil

}

Rename all someCoolErr := someCoolFuncReturningError() to simple err := someCoolFuncReturningError() to be more idiomatic.

When possible, mock using github.com/golang/mock and not custom mocks. Therefore, It'll be necessary to add some interfaces to have suitable mocks to be used in the tests.

Add an example for DynamoDB in examples like I did with s3.