Test main function for adsysd

We can do a smoke test of the main function by telling it to print the
version and asserting on the output.

cmd/adsysd/main_test.go

@@ -2,6 +2,8 @@ package main
 
 import (
 	"errors"
+	"os"
+	"os/exec"
 	"syscall"
 	"testing"
 	"time"
@@ -114,3 +116,18 @@ func TestRun(t *testing.T) {
 		})
 	}
 }
+
+func TestMainApp(t *testing.T) {
+	if os.Getenv("ADSYS_CALL_MAIN") != "" {
+		main()
+		return
+	}
+
+	// #nosec G204: this is only for tests, under controlled args
+	cmd := exec.Command(os.Args[0], "version", "-test.run=TestMainApp")
+	cmd.Env = append(os.Environ(), "ADSYS_CALL_MAIN=1")
+	out, err := cmd.CombinedOutput()
+
+	require.Contains(t, string(out), "adsysd\tdev", "Main function should print the version")
+	require.NoError(t, err, "Main should not return an error")
+}