separate main part and add tests for entire logic

main.go

@@ -51,25 +51,31 @@ func parseOptions(out io.Writer, args []string) (*options, int) {
 	return o, -1
 }
 
-func main() {
-	opts, code := parseOptions(os.Stderr, os.Args)
-	if code >= 0 {
-		os.Exit(code)
-	}
-
+func measure(opts *options, out io.Writer) error {
 	collected, err := collectMeasurements(opts)
 	if err != nil {
-		fmt.Fprintln(os.Stderr, err)
-		os.Exit(1)
+		return err
 	}
 
 	summary, err := summarizeStartuptime(collected, opts.verbose)
 	if err != nil {
+		return err
+	}
+
+	fmt.Fprintf(out, "Extra options: %v\n", opts.extraArgs)
+	fmt.Fprintf(out, "Measured: %d times\n\n", opts.count)
+	summary.print(out)
+	return nil
+}
+
+func main() {
+	opts, code := parseOptions(os.Stderr, os.Args)
+	if code >= 0 {
+		os.Exit(code)
+	}
+
+	if err := measure(opts, os.Stdout); err != nil {
 		fmt.Fprintln(os.Stderr, err)
 		os.Exit(1)
 	}
-
-	fmt.Printf("Extra options: %v\n", opts.extraArgs)
-	fmt.Printf("Measured: %d times\n\n", opts.count)
-	summary.print(os.Stdout)
 }

main_test.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"bytes"
+	"io"
 	"strings"
 	"testing"
 
@@ -62,3 +63,48 @@ func TestParseOptionsHelpOutput(t *testing.T) {
 		t.Fatal("unexpected help output to stderr:", stderr)
 	}
 }
+
+func TestRunMeasurementMainOK(t *testing.T) {
+	o := &options{
+		count:     1,
+		vimPath:   "vim",
+		script:    false,
+		extraArgs: []string{},
+		warmup:    0,
+		verbose:   false,
+	}
+
+	var b bytes.Buffer
+	if err := measure(o, &b); err != nil {
+		t.Fatal(err)
+	}
+
+	out := b.String()
+	for _, want := range []string{
+		"Extra options: []",
+		"Measured: 1 times",
+		"Total Average:",
+		"Total Max:",
+		"Total Min:",
+	} {
+		if !strings.Contains(out, want) {
+			t.Errorf("output should contain %q but got %q", want, out)
+		}
+	}
+}
+
+func TestErrorWhileRunningMain(t *testing.T) {
+	o := &options{
+		count:     1,
+		vimPath:   "this-executable-does-not-exist",
+		script:    false,
+		extraArgs: []string{},
+		warmup:    0,
+		verbose:   false,
+	}
+
+	err := measure(o, io.Discard)
+	if !strings.Contains(err.Error(), `failed to run "this-executable-does-not-exist"`) {
+		t.Fatal("error was unexpected:", err)
+	}
+}