Add subprocess runner and generated config helpers

internal/adapters/seriatim/fake_test.go

@@ -3,12 +3,21 @@ package seriatim
 import (
 	"context"
 	"errors"
+	"os"
+	"path/filepath"
+	"strings"
 	"testing"
 )
 
 func TestFakeRunnerCapturesRequestAndReturnsPath(t *testing.T) {
 	fake := &FakeRunner{}
-	req := MergeRequest{GeneratedConfigPath: "config/seriatim.yml", OutputMergedTranscriptPath: "transcripts/merged.json"}
+	dir := t.TempDir()
+	req := MergeRequest{
+		GeneratedConfigPath:        filepath.Join(dir, "config", "seriatim.yml"),
+		OutputMergedTranscriptPath: filepath.Join(dir, "transcripts", "merged.json"),
+		StdoutLogPath:              filepath.Join(dir, "logs", "seriatim.stdout.log"),
+		StderrLogPath:              filepath.Join(dir, "logs", "seriatim.stderr.log"),
+	}
 
 	res, err := fake.Run(context.Background(), req)
 	if err != nil {
@@ -20,6 +29,19 @@ func TestFakeRunnerCapturesRequestAndReturnsPath(t *testing.T) {
 	if res.MergedTranscriptPath != req.OutputMergedTranscriptPath {
 		t.Fatalf("merged path = %q, want %q", res.MergedTranscriptPath, req.OutputMergedTranscriptPath)
 	}
+
+	cfgData, err := os.ReadFile(req.GeneratedConfigPath)
+	if err != nil {
+		t.Fatalf("read generated config: %v", err)
+	}
+	if !strings.Contains(string(cfgData), "placeholder: true") {
+		t.Fatalf("generated config = %q, want placeholder marker", string(cfgData))
+	}
+	for _, logPath := range []string{req.StdoutLogPath, req.StderrLogPath} {
+		if _, err := os.Stat(logPath); err != nil {
+			t.Fatalf("expected log file %q to exist: %v", logPath, err)
+		}
+	}
 }
 
 func TestFakeRunnerError(t *testing.T) {