add endpoint to get all tags across customers (#40)

customer.go

@@ -22,6 +22,7 @@ type CustomerService interface {
 	Update(Customer) (*Customer, error)
 	Delete(int) error
 	ListOrders(int, interface{}) ([]Order, error)
+	ListTags(interface{}) ([]string, error)
 
 	// MetafieldsService used for Customer resource to communicate with Metafields resource
 	MetafieldsService
@@ -68,6 +69,11 @@ type CustomersResource struct {
 	Customers []Customer `json:"customers"`
 }
 
+// Represents the result from the customers/tags.json endpoint
+type CustomerTagsResource struct {
+	Tags []string `json:"tags"`
+}
+
 // Represents the options available when searching for a customer
 type CustomerSearchOptions struct {
 	Page   int    `url:"page,omitempty"`
@@ -174,3 +180,11 @@ func (s *CustomerServiceOp) ListOrders(customerID int, options interface{}) ([]O
 	err := s.client.Get(path, resource, options)
 	return resource.Orders, err
 }
+
+// ListTags retrieves all unique tags across all customers
+func (s *CustomerServiceOp) ListTags(options interface{}) ([]string, error) {
+	path := fmt.Sprintf("%s/tags.json", customersBasePath)
+	resource := new(CustomerTagsResource)
+	err := s.client.Get(path, resource, options)
+	return resource.Tags, err
+}

customer_test.go

@@ -449,3 +449,29 @@ func TestCustomerListOrders(t *testing.T) {
 	order := orders[0]
 	orderTests(t, order)
 }
+
+func TestCustomerListTags(t *testing.T) {
+	setup()
+	defer teardown()
+
+	httpmock.RegisterResponder(
+		"GET",
+		"https://fooshop.myshopify.com/admin/customers/tags.json",
+		httpmock.NewBytesResponder(200, loadFixture("customer_tags.json")),
+	)
+
+	tags, err := client.Customer.ListTags(nil)
+	if err != nil {
+		t.Errorf("Customer.ListTags returned error: %v", err)
+	}
+
+	// Check that tags were parsed
+	if len(tags) != 2 {
+		t.Errorf("Customer.ListTags got %v tags, expected: 2", len(tags))
+	}
+
+	// Check correct tag was read
+	if len(tags) > 0 && tags[0] != "tag1" {
+		t.Errorf("Customer.ListTags got %v as the first tag, expected: 'tag1'", tags[0])
+	}
+}

fixtures/customer_tags.json

@@ -0,0 +1,6 @@
+{
+    "tags": [
+        "tag1",
+        "another-tag"
+    ]
+}