Test that a mounted source names and reads its manifest beside its files, before or after the mount

internal/datafiles/datafiles_test.go

@@ -182,3 +182,22 @@ func TestAMountedTreeIsAValidFS(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestAMountedSourceNamesItsManifestBesideItsFiles(t *testing.T) {
+	dir := t.TempDir()
+	for name, c := range map[string]struct {
+		src  Source
+		want string
+	}{
+		"an fs.FS":    {FS(fstest.MapFS{}).Mounted("my.data"), "my/data/.fejkdata.json"},
+		"a data path": {Dir(dir).Mounted("my.data"), filepath.ToSlash(filepath.Join(dir, ".fejkdata.json"))},
+	} {
+		if got := c.src.ManifestPath(); got != c.want {
+			t.Errorf("%s: ManifestPath() = %q, want %q", name, got, c.want)
+		}
+	}
+	m, err := FS(fstest.MapFS{ManifestFile: {Data: []byte(`{"namespace": "my.data"}`)}}).Mounted("my.data").Manifest()
+	if err != nil || m.Namespace != "my.data" {
+		t.Errorf("Manifest() after Mounted = %+v, %v, want the manifest read from beside the files", m, err)
+	}
+}

shipped_test.go

@@ -597,6 +597,18 @@ func indexEntry(s categorySite) datafiles.IndexEntry {
 	return e
 }
 
+func TestAMountedIndexedCategoryWithNoFileNamesTheManifestBesideItsFiles(t *testing.T) {
+	f, err := New(WithDataFS(fstest.MapFS{
+		".fejkdata.json": {Data: []byte(`{"index": {"my.gone": {"paths": [""]}}, "namespace": "my"}`)},
+	}))
+	if err != nil {
+		t.Fatalf("New() = %v", err)
+	}
+	if _, err := f.Fake("my.gone"); err == nil || !strings.Contains(err.Error(), "my/.fejkdata.json indexes my.gone") {
+		t.Fatalf(`Fake("my.gone") = %v, want the manifest named as my/.fejkdata.json`, err)
+	}
+}
+
 func TestAnIndexedCategoryWithNoFileNamesTheManifest(t *testing.T) {
 	f, err := New(WithDataFS(fstest.MapFS{
 		".fejkdata.json": {Data: []byte(`{"index": {"gone": {"paths": [""]}}}`)},