Define adapter interfaces and fake implementations

internal/adapters/seriatim/fake_test.go

@@ -0,0 +1,31 @@
+package seriatim
+
+import (
+	"context"
+	"errors"
+	"testing"
+)
+
+func TestFakeRunnerCapturesRequestAndReturnsPath(t *testing.T) {
+	fake := &FakeRunner{}
+	req := MergeRequest{GeneratedConfigPath: "config/seriatim.yml", OutputMergedTranscriptPath: "transcripts/merged.json"}
+
+	res, err := fake.Run(context.Background(), req)
+	if err != nil {
+		t.Fatalf("Run() error = %v", err)
+	}
+	if len(fake.Requests) != 1 || fake.Requests[0].GeneratedConfigPath == "" {
+		t.Fatalf("requests = %#v, want captured request", fake.Requests)
+	}
+	if res.MergedTranscriptPath != req.OutputMergedTranscriptPath {
+		t.Fatalf("merged path = %q, want %q", res.MergedTranscriptPath, req.OutputMergedTranscriptPath)
+	}
+}
+
+func TestFakeRunnerError(t *testing.T) {
+	fake := &FakeRunner{Err: errors.New("boom")}
+	_, err := fake.Run(context.Background(), MergeRequest{})
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+}