Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/tests/tests.go

@@ -0,0 +1,72 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+//go:build integration
+// +build integration
+
+package tests
+
+import (
+	"math/rand"
+	"strconv"
+	"strings"
+	"testing"
+
+	miniflux "miniflux.app/v2/client"
+)
+
+const (
+	testBaseURL           = "http://127.0.0.1:8080/"
+	testAdminUsername     = "admin"
+	testAdminPassword     = "test123"
+	testStandardPassword  = "secret"
+	testFeedURL           = "https://miniflux.app/feed.xml"
+	testFeedTitle         = "Miniflux"
+	testSubscriptionTitle = "Miniflux Releases"
+	testWebsiteURL        = "https://miniflux.app"
+)
+
+func getRandomUsername() string {
+	var suffix []string
+	for i := 0; i < 10; i++ {
+		suffix = append(suffix, strconv.Itoa(rand.Intn(1000)))
+	}
+	return "user" + strings.Join(suffix, "")
+}
+
+func createClient(t *testing.T) *miniflux.Client {
+	username := getRandomUsername()
+	client := miniflux.New(testBaseURL, testAdminUsername, testAdminPassword)
+	_, err := client.CreateUser(username, testStandardPassword, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return miniflux.New(testBaseURL, username, testStandardPassword)
+}
+
+func createFeed(t *testing.T, client *miniflux.Client) (*miniflux.Feed, *miniflux.Category) {
+	categories, err := client.Categories()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	feedID, err := client.CreateFeed(&miniflux.FeedCreationRequest{
+		FeedURL:    testFeedURL,
+		CategoryID: categories[0].ID,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if feedID == 0 {
+		t.Fatalf(`Invalid feed ID, got %q`, feedID)
+	}
+
+	feed, err := client.Feed(feedID)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return feed, categories[0]
+}