Print the byte unit once in the summary line (closes #17)

formatBytes already ends in a unit, so the summary line read "9 B
bytes" or "1.0 KiB bytes". The format string in Stats.Print no longer
adds the word "bytes".

Print now takes the io.Writer to print to; its callers pass os.Stderr,
and the new test passes a buffer to read the line for one small and
one large byte count.

Model: opus-5-5

TODO.md

@@ -25,6 +25,8 @@ today), `.dockerignore`, `.gitea/workflows/check.yml` and
 
 # Completed Steps
 
+* 2026-10-06: the summary line after `sum`, `check` and `clear` prints
+    the byte unit once (`1.5 KiB`, not `1.5 KiB bytes`)
 * 2026-10-06: lint and test run as phases of the `Dockerfile`, and the
     build stage depends on both; `script/lint` and `script/test` each
     build their phase with `--no-cache`; `script/cibuild` bootstraps,

attrsum.go

@@ -71,13 +71,13 @@ func (s *Stats) Duration() time.Duration {
 	return time.Since(s.StartTime)
 }
 
-func (s *Stats) Print(opts *options, operation string) {
+func (s *Stats) Print(w io.Writer, opts *options, operation string) {
 	if opts.quiet {
 		return
 	}
 
-	fmt.Fprintf(os.Stderr,
-		"\n%s complete: %d files processed, %d skipped, %d failed, %s bytes in %s\n",
+	_, _ = fmt.Fprintf(w,
+		"\n%s complete: %d files processed, %d skipped, %d failed, %s in %s\n",
 		operation,
 		s.FilesProcessed,
 		s.FilesSkipped,
@@ -227,7 +227,7 @@ func runOverPaths(
 	}
 
 	finishBar(bar)
-	stats.Print(opts, op)
+	stats.Print(os.Stderr, opts, op)
 
 	return nil
 }
@@ -481,7 +481,7 @@ func runCheck(opts *options, args []string, cont bool) error {
 		if perr != nil {
 			if !cont {
 				finishBar(bar)
-				stats.Print(opts, "check")
+				stats.Print(os.Stderr, opts, "check")
 
 				return perr
 			}
@@ -491,7 +491,7 @@ func runCheck(opts *options, args []string, cont bool) error {
 	}
 
 	finishBar(bar)
-	stats.Print(opts, "check")
+	stats.Print(os.Stderr, opts, "check")
 
 	return finalErr
 }

attrsum_test.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bytes"
 	"errors"
 	"os"
 	"path/filepath"
@@ -328,3 +329,27 @@ func TestCheckContinuePastUnreadable(t *testing.T) {
 		t.Fatalf("expected verification error from runCheck, got %v", err)
 	}
 }
+
+func TestSummaryPrintsByteUnitOnce(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		bytesProcessed int64
+		want           string
+	}{
+		{9, ", 9 B in "},
+		{1536, ", 1.5 KiB in "},
+	}
+
+	for _, tt := range tests {
+		var out bytes.Buffer
+
+		stats := newTestStats()
+		stats.BytesProcessed = tt.bytesProcessed
+		stats.Print(&out, &options{}, "check")
+
+		if !strings.Contains(out.String(), tt.want) {
+			t.Errorf("summary %q does not contain %q", out.String(), tt.want)
+		}
+	}
+}