Add a -test flag

This allows verifying the syntax of a crontab, without running it.

README.md

@@ -204,6 +204,13 @@ WARN[2017-07-11T12:24:32+02:00] job took too long to run: it should have started
 ```
 
 
+## Testing your crontab
+
+Use the `-test` flag to prompt Supercronic to verify your crontab, but not
+execute it. This is useful as part of e.g. a build process to verify the syntax
+of your crontab.
+
+
 ## Questions and Support ###
 
 Please feel free to open an issue in this repository if you have any question

integration/invalid.crontab

@@ -0,0 +1 @@
+oops

integration/test.bats

@@ -77,3 +77,16 @@ wait_for() {
 
   wait_for grep "$canary" "$out"
 }
+
+@test "it tests a valid crontab" {
+  timeout 1s "${BATS_TEST_DIRNAME}/../supercronic" -test "${BATS_TEST_DIRNAME}/noop.crontab"
+}
+
+@test "it tests an invalid crontab" {
+  run timeout 1s "${BATS_TEST_DIRNAME}/../supercronic" -test "${BATS_TEST_DIRNAME}/invalid.crontab"
+  [[ "$status" -eq 1 ]]
+}
+
+@test "it errors on an invalid crontab" {
+  ! run_supercronic -test "${BATS_TEST_DIRNAME}/invalid.crontab"
+}

main.go

@@ -21,6 +21,7 @@ var Usage = func() {
 func main() {
 	debug := flag.Bool("debug", false, "enable debug logging")
 	json := flag.Bool("json", false, "enable JSON logging")
+	test := flag.Bool("test", false, "test crontab (does not run jobs)")
 	flag.Parse()
 
 	if *debug {
@@ -49,6 +50,12 @@ func main() {
 		return
 	}
 
+	if *test {
+		logrus.Info("crontab is valid")
+		os.Exit(0)
+		return
+	}
+
 	var wg sync.WaitGroup
 	exitCtx, notifyExit := context.WithCancel(context.Background())