Add --ignore-non-json-output-lines option

--ignore-non-json-output-lines causes gotestsum to write non-JSON test
output lines to os.Stderr instead of failing.

cmd/main.go

@@ -59,6 +59,8 @@ func setupFlags(name string) (*pflag.FlagSet, *options) {
 		"print format of test input")
 	flags.BoolVar(&opts.rawCommand, "raw-command", false,
 		"don't prepend 'go test -json' to the 'go test' command")
+	flags.BoolVar(&opts.ignoreNonJSONOutputLines, "ignore-non-json-output-lines", false,
+		"write non-JSON 'go test' output lines to stderr instead of failing")
 	flags.StringVar(&opts.jsonFile, "jsonfile",
 		lookEnvWithDefault("GOTESTSUM_JSONFILE", ""),
 		"write all TestEvents to file")
@@ -138,6 +140,7 @@ type options struct {
 	format                       string
 	debug                        bool
 	rawCommand                   bool
+	ignoreNonJSONOutputLines     bool
 	jsonFile                     string
 	junitFile                    string
 	postRunHookCmd               *commandValue
@@ -194,10 +197,11 @@ func run(opts *options) error {
 	}
 	defer handler.Close() // nolint: errcheck
 	cfg := testjson.ScanConfig{
-		Stdout:  goTestProc.stdout,
-		Stderr:  goTestProc.stderr,
-		Handler: handler,
-		Stop:    cancel,
+		Stdout:                   goTestProc.stdout,
+		Stderr:                   goTestProc.stderr,
+		Handler:                  handler,
+		Stop:                     cancel,
+		IgnoreNonJSONOutputLines: opts.ignoreNonJSONOutputLines,
 	}
 	exec, err := testjson.ScanTestOutput(cfg)
 	if err != nil {

cmd/testdata/gotestsum-help-text

@@ -6,6 +6,7 @@ Flags:
       --debug                                       enabled debug logging
   -f, --format string                               print format of test input (default "short")
       --hide-summary summary                        hide sections of the summary: skipped,failed,errors,output (default none)
+      --ignore-non-json-output-lines                write non-JSON 'go test' output lines to stderr instead of failing
       --jsonfile string                             write all TestEvents to file
       --junitfile string                            write a JUnit XML file
       --junitfile-testcase-classname field-format   format the testcase classname field as: full, relative, short (default full)

testjson/execution.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"os"
 	"sort"
 	"strings"
 	"sync"
@@ -590,6 +591,9 @@ type ScanConfig struct {
 	Execution *Execution
 	// Stop is called when ScanTestOutput fails during a scan.
 	Stop func()
+	// IgnoreNonJSONOutputLines causes ScanTestOutput to print non-JSON lines to
+	// stderr rather than returning an error.
+	IgnoreNonJSONOutputLines bool
 }
 
 // EventHandler is called by ScanTestOutput for each event and write to stderr.
@@ -662,6 +666,10 @@ func readStdout(config ScanConfig, execution *Execution) error {
 			config.Handler.Err(errBadEvent.Error() + ": " + scanner.Text())
 			continue
 		case err != nil:
+			if config.IgnoreNonJSONOutputLines {
+				fmt.Fprintf(os.Stderr, "%s\n", raw)
+				continue
+			}
 			return errors.Wrapf(err, "failed to parse test output: %s", string(raw))
 		}