add test for the command line usage

The flags and their defaults are part of the klog API and must not change.

klog_test.go

@@ -764,6 +764,9 @@ func TestFileSizeCheck(t *testing.T) {
 }
 
 func TestInitFlags(t *testing.T) {
+	defer CaptureState().Restore()
+	setFlags()
+
 	fs1 := flag.NewFlagSet("test1", flag.PanicOnError)
 	InitFlags(fs1)
 	fs1.Set("log_dir", "/test1")
@@ -779,6 +782,48 @@ func TestInitFlags(t *testing.T) {
 	}
 }
 
+func TestCommandLine(t *testing.T) {
+	var fs flag.FlagSet
+	InitFlags(&fs)
+
+	expectedFlags := `  -add_dir_header
+    	If true, adds the file directory to the header of the log messages
+  -alsologtostderr
+    	log to standard error as well as files (no effect when -logtostderr=true)
+  -log_backtrace_at value
+    	when logging hits line file:N, emit a stack trace
+  -log_dir string
+    	If non-empty, write log files in this directory (no effect when -logtostderr=true)
+  -log_file string
+    	If non-empty, use this log file (no effect when -logtostderr=true)
+  -log_file_max_size uint
+    	Defines the maximum size a log file can grow to (no effect when -logtostderr=true). Unit is megabytes. If the value is 0, the maximum file size is unlimited. (default 1800)
+  -logtostderr
+    	log to standard error instead of files (default true)
+  -one_output
+    	If true, only write logs to their native severity level (vs also writing to each lower severity level; no effect when -logtostderr=true)
+  -skip_headers
+    	If true, avoid header prefixes in the log messages
+  -skip_log_headers
+    	If true, avoid headers when opening log files (no effect when -logtostderr=true)
+  -stderrthreshold value
+    	logs at or above this threshold go to stderr when writing to files and stderr (no effect when -logtostderr=true or -alsologtostderr=false) (default 2)
+  -v value
+    	number for the log level verbosity
+  -vmodule value
+    	comma-separated list of pattern=N settings for file-filtered logging
+`
+
+	var output bytes.Buffer
+	fs.SetOutput(&output)
+	fs.PrintDefaults()
+	actualFlags := output.String()
+
+	if expectedFlags != actualFlags {
+		t.Fatalf("Command line changed.\nExpected:\n%q\nActual:\n%q\n", expectedFlags, actualFlags)
+	}
+}
+
 func TestInfoObjectRef(t *testing.T) {
 	defer CaptureState().Restore()
 	setFlags()