fix: resolve golangci-lint errcheck and staticcheck warnings

Use t.Setenv in tests, add error return handling, and replace
WriteString(fmt.Sprintf(...)) with fmt.Fprintf.

internal/config/config_test.go

@@ -7,9 +7,9 @@ import (
 
 func TestLoad(t *testing.T) {
 	// Clear environment variables for clean test
-	os.Unsetenv("PORT")
+	_ = os.Unsetenv("PORT")
-	os.Unsetenv("HOST")
+	_ = os.Unsetenv("HOST")
-	os.Unsetenv("GO_ENV")
+	_ = os.Unsetenv("GO_ENV")
 
 	cfg := Load()
 
@@ -41,16 +41,10 @@ func TestLoad(t *testing.T) {
 
 func TestLoadWithEnvVars(t *testing.T) {
 	// Set custom environment variables
-	os.Setenv("PORT", "8080")
+	t.Setenv("PORT", "8080")
-	os.Setenv("HOST", "0.0.0.0")
+	t.Setenv("HOST", "0.0.0.0")
-	os.Setenv("READ_TIMEOUT", "30")
+	t.Setenv("READ_TIMEOUT", "30")
-	os.Setenv("WRITE_TIMEOUT", "45")
+	t.Setenv("WRITE_TIMEOUT", "45")
-	defer func() {
-		os.Unsetenv("PORT")
-		os.Unsetenv("HOST")
-		os.Unsetenv("READ_TIMEOUT")
-		os.Unsetenv("WRITE_TIMEOUT")
-	}()
 
 	cfg := Load()
 
@@ -72,8 +66,8 @@ func TestLoadWithEnvVars(t *testing.T) {
 }
 
 func TestAddress(t *testing.T) {
-	os.Unsetenv("PORT")
+	_ = os.Unsetenv("PORT")
-	os.Unsetenv("HOST")
+	_ = os.Unsetenv("HOST")
 
 	cfg := Load()
 	addr := cfg.Address()
@@ -83,12 +77,8 @@ func TestAddress(t *testing.T) {
 	}
 
 	// Test with custom values
-	os.Setenv("PORT", "3000")
+	t.Setenv("PORT", "3000")
-	os.Setenv("HOST", "127.0.0.1")
+	t.Setenv("HOST", "127.0.0.1")
-	defer func() {
-		os.Unsetenv("PORT")
-		os.Unsetenv("HOST")
-	}()
 
 	cfg = Load()
 	addr = cfg.Address()
@@ -100,8 +90,7 @@ func TestAddress(t *testing.T) {
 
 func TestGetEnv(t *testing.T) {
 	// Test with existing var
-	os.Setenv("TEST_VAR", "test_value")
+	t.Setenv("TEST_VAR", "test_value")
-	defer os.Unsetenv("TEST_VAR")
 
 	result := getEnv("TEST_VAR", "default")
 	if result != "test_value" {
@@ -117,8 +106,7 @@ func TestGetEnv(t *testing.T) {
 
 func TestGetEnvAsInt(t *testing.T) {
 	// Test with valid int
-	os.Setenv("INT_VAR", "42")
+	t.Setenv("INT_VAR", "42")
-	defer os.Unsetenv("INT_VAR")
 
 	result := getEnvAsInt("INT_VAR", 10)
 	if result != 42 {
@@ -126,8 +114,7 @@ func TestGetEnvAsInt(t *testing.T) {
 	}
 
 	// Test with invalid int
-	os.Setenv("INVALID_INT", "not_a_number")
+	t.Setenv("INVALID_INT", "not_a_number")
-	defer os.Unsetenv("INVALID_INT")
 
 	result = getEnvAsInt("INVALID_INT", 10)
 	if result != 10 {
@@ -158,8 +145,7 @@ func TestGetEnvAsBool(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			os.Setenv("BOOL_VAR", tt.envValue)
+			t.Setenv("BOOL_VAR", tt.envValue)
-			defer os.Unsetenv("BOOL_VAR")
 
 			result := getEnvAsBool("BOOL_VAR", tt.defaultValue)
 			if result != tt.expected {
@@ -192,11 +178,10 @@ func TestIsDevelopment(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			if tt.envValue == "" {
-				os.Unsetenv("GO_ENV")
+				_ = os.Unsetenv("GO_ENV")
 			} else {
-				os.Setenv("GO_ENV", tt.envValue)
+				t.Setenv("GO_ENV", tt.envValue)
 			}
-			defer os.Unsetenv("GO_ENV")
 
 			result := isDevelopment()
 			if result != tt.expected {
@@ -208,9 +193,8 @@ func TestIsDevelopment(t *testing.T) {
 
 func TestTemplateHotReload(t *testing.T) {
 	// In development, hot reload should be true by default
-	os.Setenv("GO_ENV", "development")
+	t.Setenv("GO_ENV", "development")
-	os.Unsetenv("TEMPLATE_HOT_RELOAD")
+	_ = os.Unsetenv("TEMPLATE_HOT_RELOAD")
-	defer os.Unsetenv("GO_ENV")
 
 	cfg := Load()
 	if !cfg.Template.HotReload {
@@ -218,8 +202,7 @@ func TestTemplateHotReload(t *testing.T) {
 	}
 
 	// Explicit false should override
-	os.Setenv("TEMPLATE_HOT_RELOAD", "false")
+	t.Setenv("TEMPLATE_HOT_RELOAD", "false")
-	defer os.Unsetenv("TEMPLATE_HOT_RELOAD")
 
 	cfg = Load()
 	if cfg.Template.HotReload {
@@ -227,8 +210,8 @@ func TestTemplateHotReload(t *testing.T) {
 	}
 
 	// In production, hot reload should be false by default
-	os.Setenv("GO_ENV", "production")
+	t.Setenv("GO_ENV", "production")
-	os.Unsetenv("TEMPLATE_HOT_RELOAD")
+	_ = os.Unsetenv("TEMPLATE_HOT_RELOAD")
 
 	cfg = Load()
 	if cfg.Template.HotReload {
@@ -237,10 +220,10 @@ func TestTemplateHotReload(t *testing.T) {
 }
 
 func TestEmailConfig(t *testing.T) {
-	os.Unsetenv("SMTP_HOST")
+	_ = os.Unsetenv("SMTP_HOST")
-	os.Unsetenv("SMTP_PORT")
+	_ = os.Unsetenv("SMTP_PORT")
-	os.Unsetenv("SMTP_USER")
+	_ = os.Unsetenv("SMTP_USER")
-	os.Unsetenv("SMTP_PASSWORD")
+	_ = os.Unsetenv("SMTP_PASSWORD")
 
 	cfg := Load()
 
@@ -254,12 +237,8 @@ func TestEmailConfig(t *testing.T) {
 	}
 
 	// Test custom values
-	os.Setenv("SMTP_HOST", "mail.example.com")
+	t.Setenv("SMTP_HOST", "mail.example.com")
-	os.Setenv("SMTP_PORT", "465")
+	t.Setenv("SMTP_PORT", "465")
-	defer func() {
-		os.Unsetenv("SMTP_HOST")
-		os.Unsetenv("SMTP_PORT")
-	}()
 
 	cfg = Load()
 	if cfg.Email.SMTPHost != "mail.example.com" {

internal/email/email.go

@@ -303,19 +303,19 @@ func (e *Service) formatMultipartMessage(from, to, replyTo, subject, htmlBody, t
 	var message strings.Builder
 
 	// Headers
-	message.WriteString(fmt.Sprintf("From: %s\r\n", from))
+	fmt.Fprintf(&message, "From: %s\r\n", from)
-	message.WriteString(fmt.Sprintf("To: %s\r\n", to))
+	fmt.Fprintf(&message, "To: %s\r\n", to)
 	if replyTo != "" {
-		message.WriteString(fmt.Sprintf("Reply-To: %s\r\n", replyTo))
+		fmt.Fprintf(&message, "Reply-To: %s\r\n", replyTo)
 	}
-	message.WriteString(fmt.Sprintf("Subject: %s\r\n", subject))
+	fmt.Fprintf(&message, "Subject: %s\r\n", subject)
 	message.WriteString("MIME-Version: 1.0\r\n")
-	message.WriteString(fmt.Sprintf("Content-Type: multipart/alternative; boundary=\"%s\"\r\n", boundary))
+	fmt.Fprintf(&message, "Content-Type: multipart/alternative; boundary=\"%s\"\r\n", boundary)
-	message.WriteString(fmt.Sprintf("Date: %s\r\n", time.Now().Format(time.RFC1123Z)))
+	fmt.Fprintf(&message, "Date: %s\r\n", time.Now().Format(time.RFC1123Z))
 	message.WriteString("\r\n")
 
 	// Plain text part
-	message.WriteString(fmt.Sprintf("--%s\r\n", boundary))
+	fmt.Fprintf(&message, "--%s\r\n", boundary)
 	message.WriteString("Content-Type: text/plain; charset=\"utf-8\"\r\n")
 	message.WriteString("Content-Transfer-Encoding: quoted-printable\r\n")
 	message.WriteString("\r\n")
@@ -323,7 +323,7 @@ func (e *Service) formatMultipartMessage(from, to, replyTo, subject, htmlBody, t
 	message.WriteString("\r\n")
 
 	// HTML part
-	message.WriteString(fmt.Sprintf("--%s\r\n", boundary))
+	fmt.Fprintf(&message, "--%s\r\n", boundary)
 	message.WriteString("Content-Type: text/html; charset=\"utf-8\"\r\n")
 	message.WriteString("Content-Transfer-Encoding: base64\r\n")
 	message.WriteString("\r\n")
@@ -340,7 +340,7 @@ func (e *Service) formatMultipartMessage(from, to, replyTo, subject, htmlBody, t
 	}
 
 	// End boundary
-	message.WriteString(fmt.Sprintf("--%s--\r\n", boundary))
+	fmt.Fprintf(&message, "--%s--\r\n", boundary)
 
 	return message.String()
 }

internal/handlers/cv_pages_test.go

@@ -128,7 +128,7 @@ func TestDefaultCVShortcut(t *testing.T) {
 	if err != nil || resp.StatusCode != http.StatusOK {
 		t.Skip("Skipping PDF generation test - server not running on localhost:1999")
 	}
-	resp.Body.Close()
+	_ = resp.Body.Close()
 
 	handler := newTestCVHandler(t, "localhost:1999", nil)