Testing with Elastic

logic.go

package esi

import (
	"context"

	"github.com/olivere/elastic"
)

type BusinessLogic struct {
	s Searcher
}

func (bl *BusinessLogic) Search() (*elastic.SearchResult, error) {
	return bl.s.Do(context.TODO())
}

logic_test.go

package esi

import (
	"context"
	"testing"

	"github.com/olivere/elastic"
)

func TestBusinessLogic(t *testing.T) {
	mock := &MockSearcher{}
	mock.OnDo = func(_ context.Context) (*elastic.SearchResult, error) {
		return &elastic.SearchResult{}, nil
	}
	//
	bl := &BusinessLogic{
		s: mock,
	}
	res, err := bl.Search()
	if err != nil {
		t.Fatal(err)
	}
	if res == nil {
		t.Fatal("expected search result")
	}
}

searcher.go

package esi

import (
	"context"

	"github.com/olivere/elastic"
)

// Notice that *elastic.SearchService implements the Searcher interface!

type Searcher interface {
	Do(ctx context.Context) (*elastic.SearchResult, error)
}

searcher_mock.go

package esi

import (
	"context"

	"github.com/olivere/elastic"
)

var (
	// Compile-time error when *MockServer doesn't implement Searcher interface
	_ Searcher = (*MockSearcher)(nil)
)

type MockSearcher struct {
	OnDo func(ctx context.Context) (*elastic.SearchResult, error)
}

func (s *MockSearcher) Do(ctx context.Context) (*elastic.SearchResult, error) {
	return s.OnDo(ctx)
}