Fix all usetesting linter errors

- Replace os.MkdirTemp() with t.TempDir() in test files
- Replace os.Setenv() with t.Setenv() in test files
- Remove manual environment cleanup code (t.Setenv automatically restores)
- Remove unused "os" imports from files that no longer use os package

internal/cli/cli_test.go

@@ -37,19 +37,9 @@ func TestCLIInstanceWithFs(t *testing.T) {
 func TestDetermineStateDir(t *testing.T) {
 	// Test the determineStateDir function from the secret package
 
-	// Save original environment and restore it after test
-	originalStateDir := os.Getenv(secret.EnvStateDir)
-	defer func() {
-		if originalStateDir == "" {
-			os.Unsetenv(secret.EnvStateDir)
-		} else {
-			os.Setenv(secret.EnvStateDir, originalStateDir)
-		}
-	}()
-
 	// Test with environment variable set
 	testEnvDir := "/test-env-dir"
-	os.Setenv(secret.EnvStateDir, testEnvDir)
+	t.Setenv(secret.EnvStateDir, testEnvDir)
 
 	stateDir := secret.DetermineStateDir("")
 	if stateDir != testEnvDir {

internal/cli/generate.go

@@ -28,7 +28,8 @@ func newGenerateMnemonicCmd() *cobra.Command {
 	return &cobra.Command{
 		Use:   "mnemonic",
 		Short: "Generate a random BIP39 mnemonic phrase",
-		Long:  `Generate a cryptographically secure random BIP39 mnemonic phrase that can be used with 'secret init' or 'secret import'.`,
+		Long: `Generate a cryptographically secure random BIP39 mnemonic phrase that can be used with ` +
+			`'secret init' or 'secret import'.`,
 		RunE: func(cmd *cobra.Command, args []string) error {
 			cli := NewCLIInstance()
 			return cli.GenerateMnemonic(cmd)

internal/cli/integration_test.go

@@ -52,8 +52,7 @@ func TestMain(m *testing.M) {
 // This test serves as both validation and documentation of the program's behavior.
 func TestSecretManagerIntegration(t *testing.T) {
 	// Enable debug logging to diagnose issues
-	os.Setenv("GODEBUG", "berlin.sneak.pkg.secret")
-	defer os.Unsetenv("GODEBUG")
+	t.Setenv("GODEBUG", "berlin.sneak.pkg.secret")
 
 	// Reinitialize debug logging to pick up the environment variable change
 	secret.InitDebugLogging()
@@ -66,8 +65,7 @@ func TestSecretManagerIntegration(t *testing.T) {
 	tempDir := t.TempDir()
 
 	// Set environment variables for the test
-	os.Setenv("SB_SECRET_STATE_DIR", tempDir)
-	defer os.Unsetenv("SB_SECRET_STATE_DIR")
+	t.Setenv("SB_SECRET_STATE_DIR", tempDir)
 
 	// Find the secret binary path (needed for tests that still use exec.Command)
 	wd, err := os.Getwd()
@@ -1570,7 +1568,7 @@ func test23ErrorHandling(t *testing.T, tempDir, secretPath, testMnemonic string,
 	cmdOutput, err = cmd.CombinedOutput()
 	assert.Error(t, err, "get without mnemonic should fail")
 	assert.Contains(t, string(cmdOutput), "failed to unlock", "should indicate unlock failure")
-	os.Setenv("SB_SECRET_MNEMONIC", unsetMnemonic)
+	t.Setenv("SB_SECRET_MNEMONIC", unsetMnemonic)
 
 	// Invalid secret names (already tested in test 12)