cmd(version): check for more errors in the test

cmd/version_test.go

@@ -5,6 +5,7 @@ package cmd
 
 import (
 	"bytes"
+	"errors"
 	"os"
 	"regexp"
 	"testing"
@@ -17,9 +18,13 @@ func TestNixFlake_GosrcVersionStringEquivalence(t *testing.T) {
 
 	fData, err := os.ReadFile("../flake.nix")
 	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
 			t.Errorf("Failed to open flake.nix: %q", err)
 		}
 
+		t.Errorf("Error reading flake: %q", err)
+	}
+
 	got := bytes.Contains(fData, []byte("      version = \""+want+"\""))
 
 	if !got {