diff --git a/config/config_test.go b/config/config_test.go
new file mode 100644
index 0000000..ad13382
--- /dev/null
+++ b/config/config_test.go
@@ -0,0 +1,67 @@
+package config
+
+import "testing"
+
+func TestGetValueOrDefaultBoolean(t *testing.T) {
+	tests := []struct {
+		name         string
+		value        string
+		defaultValue bool
+		want         bool
+	}{
+		{name: "default true", defaultValue: true, want: true},
+		{name: "default false", defaultValue: false, want: false},
+		{name: "explicit true", value: "true", want: true},
+		{name: "explicit false", value: "false", defaultValue: true, want: false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := getValueOrDefaultBoolean(tt.value, tt.defaultValue); got != tt.want {
+				t.Fatalf("getValueOrDefaultBoolean() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestGetValueOrDefaultInt(t *testing.T) {
+	tests := []struct {
+		name         string
+		value        string
+		defaultValue int
+		want         int
+	}{
+		{name: "default", defaultValue: 3000, want: 3000},
+		{name: "configured", value: "8080", defaultValue: 3000, want: 8080},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := getValueOrDefaultInt(tt.value, tt.defaultValue); got != tt.want {
+				t.Fatalf("getValueOrDefaultInt() = %d, want %d", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestDefaultConfigs(t *testing.T) {
+	for _, key := range []string{
+		"ENV", "PORT", "IS_DB_SEEDED", "IS_RATE_LIMITER_ENABLED",
+		"THREADS_MAX_COUNT", "THREAD_BUMP_LIMIT", "IS_CAPTCHA_ACTIVE",
+		"GATEWAY_URL", "GATEWAY_API_KEY", "GATEWAY_BOARD_ID",
+		"GATEWAY_BOARD_URL", "GATEWAY_BOARD_DESCRIPTION", "POSTGRES_URL",
+	} {
+		t.Setenv(key, "")
+	}
+
+	app := getAppConfig()
+	if app.Env != "release" || app.Port != 3000 || app.IsDbSeeded {
+		t.Fatalf("unexpected app defaults: %+v", app)
+	}
+	if !app.IsRateLimiterEnabled || app.ThreadsMaxCount != 50 || app.ThreadBumpLimit != 500 || !app.IsCaptchaActive {
+		t.Fatalf("unexpected feature defaults: %+v", app)
+	}
+	if db := getDbConfig(); db.Url != "postgresql://localhost/micrach" {
+		t.Fatalf("unexpected database default: %+v", db)
+	}
+}
diff --git a/controllers/threads_controller_test.go b/controllers/threads_controller_test.go
new file mode 100644
index 0000000..2e6cff3
--- /dev/null
+++ b/controllers/threads_controller_test.go
@@ -0,0 +1,46 @@
+package controllers
+
+import (
+	"io"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gofiber/fiber/v2"
+)
+
+type testViews struct{}
+
+func (testViews) Load() error { return nil }
+
+func (testViews) Render(out io.Writer, name string, _ interface{}, _ ...string) error {
+	_, err := io.WriteString(out, name)
+	return err
+}
+
+func TestGetThreadsRejectsInvalidPage(t *testing.T) {
+	app := fiber.New(fiber.Config{Views: testViews{}})
+	app.Get("/", GetThreads)
+
+	resp, err := app.Test(httptest.NewRequest("GET", "/?page=0", nil))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != fiber.StatusNotFound {
+		t.Fatalf("status = %d, want %d", resp.StatusCode, fiber.StatusNotFound)
+	}
+}
+
+func TestGetThreadRejectsInvalidID(t *testing.T) {
+	app := fiber.New(fiber.Config{Views: testViews{}})
+	app.Get("/:threadID", GetThread)
+
+	resp, err := app.Test(httptest.NewRequest("GET", "/invalid", nil))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != fiber.StatusNotFound {
+		t.Fatalf("status = %d, want %d", resp.StatusCode, fiber.StatusNotFound)
+	}
+}
diff --git a/utils/utils_test.go b/utils/utils_test.go
new file mode 100644
index 0000000..1f58b11
--- /dev/null
+++ b/utils/utils_test.go
@@ -0,0 +1,48 @@
+package utils
+
+import (
+	"mime/multipart"
+	"net/textproto"
+	"strings"
+	"testing"
+
+	"micrach/repositories"
+)
+
+func fileHeader(contentType string, size int64) *multipart.FileHeader {
+	header := make(textproto.MIMEHeader)
+	header.Set("Content-Type", contentType)
+	return &multipart.FileHeader{Filename: "upload", Header: header, Size: size}
+}
+
+func TestValidatePost(t *testing.T) {
+	validPNG := fileHeader("image/png", 1)
+	validJPEG := fileHeader("image/jpeg", FILE_SIZE_IN_BYTES)
+
+	tests := []struct {
+		name  string
+		title string
+		text  string
+		files []*multipart.FileHeader
+		want  string
+	}{
+		{name: "text only", text: "hello"},
+		{name: "file only", files: []*multipart.FileHeader{validPNG}},
+		{name: "empty", want: repositories.InvalidTextOrFilesErrorMessage},
+		{name: "title over limit", title: strings.Repeat("я", 101), text: "ok", want: repositories.InvalidTitleLengthErrorMessage},
+		{name: "text over limit", text: strings.Repeat("я", 1001), want: repositories.InvalidTextLengthErrorMessage},
+		{name: "four files", files: []*multipart.FileHeader{validPNG, validPNG, validJPEG, validJPEG}},
+		{name: "five files", files: []*multipart.FileHeader{validPNG, validPNG, validPNG, validPNG, validPNG}, want: repositories.InvalidFilesLengthErrorMessage},
+		{name: "unsupported content type", files: []*multipart.FileHeader{fileHeader("image/gif", 1)}, want: repositories.InvalidFileExtErrorMessage},
+		{name: "size at limit", files: []*multipart.FileHeader{validJPEG}},
+		{name: "size over limit", files: []*multipart.FileHeader{fileHeader("image/jpeg", FILE_SIZE_IN_BYTES+1)}, want: repositories.InvalidFileSizeErrorMessage},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := ValidatePost(tt.title, tt.text, tt.files); got != tt.want {
+				t.Fatalf("ValidatePost() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}