Fix tealang CLI segfault

* Add a CLI unit test
* Closes #6

main.go

@@ -53,7 +53,7 @@ Syntax highlighter for vscode: https://github.com/pzbitskiy/tealang-syntax-highl
 		if inFile == "-" {
 			data, err := ioutil.ReadAll(os.Stdin)
 			if err != nil {
-				fmt.Printf(err.Error())
+				fmt.Println(err.Error())
 				os.Exit(1)
 			}
 			source = string(data)
@@ -124,10 +124,9 @@ Syntax highlighter for vscode: https://github.com/pzbitskiy/tealang-syntax-highl
 				fmt.Println(err.Error())
 				os.Exit(1)
 			}
+			bytecode = op.Program
 		}
 
-		bytecode = op.Program
-
 		if stdout {
 			output := teal
 			if bytecode != nil {
@@ -183,14 +182,18 @@ Syntax highlighter for vscode: https://github.com/pzbitskiy/tealang-syntax-highl
 	},
 }
 
-func main() {
+func setRootCmdFlags() {
 	rootCmd.Flags().StringVarP(&outFile, "output", "o", "", "write output to this file")
 	rootCmd.Flags().BoolVarP(&compileOnly, "compile", "c", false, "compile to TEAL assembler, do not produce bytecode")
 	rootCmd.Flags().BoolVarP(&verbose, "verbose", "v", false, "verbose output")
 	rootCmd.Flags().StringVarP(&oneliner, "oneliner", "l", "", "compile logic one-liner like '(txn.Sender == \"abc\") && (1+2) >= 3'")
 	rootCmd.Flags().BoolVarP(&stdout, "stdout", "s", false, "write output to stdout instead of a file")
 	rootCmd.Flags().BoolVarP(&raw, "raw", "r", false, "do not hex-encode bytecode when outputting to stdout")
 	rootCmd.Flags().StringVarP(&dryrun, "dryrun", "d", "", "dry run program with transaction data from the file provided")
+}
+
+func main() {
+	setRootCmdFlags()
 
 	if err := rootCmd.Execute(); err != nil {
 		fmt.Println(err)

main_test.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestMainBasic(t *testing.T) {
+	setRootCmdFlags()
+
+	old := os.Stdout
+	r, w, _ := os.Pipe()
+	os.Stdout = w
+	defer func() {
+		os.Stdout = old
+	}()
+
+	rootCmd.SetArgs([]string{"-c", "examples/basic.tl", "-s"})
+
+	err := rootCmd.Execute()
+	require.NoError(t, err)
+	w.Close()
+
+	out, err := ioutil.ReadAll(r)
+	require.NoError(t, err)
+	require.Contains(t, string(out), "end_main")
+}