Added shared helper for module prompt FS

internal/modules/sharedassets/prompt_fs_test.go

@@ -0,0 +1,77 @@
+package sharedassets
+
+import (
+	"io/fs"
+	"strings"
+	"testing"
+	"testing/fstest"
+)
+
+func TestModulePromptFSCombinesModuleAndSharedPrompts(t *testing.T) {
+	fsys, err := ModulePromptFS("dnd.test", fstest.MapFS{
+		"assets/prompts/dnd.test.yaml": {Data: []byte("id: dnd.test")},
+		"assets/prompts/task.md":       {Data: []byte("task")},
+	}, []ModulePromptFile{
+		{Name: "dnd.test.yaml", Path: "assets/prompts/dnd.test.yaml"},
+		{Name: "task.md", Path: "assets/prompts/task.md"},
+	})
+	if err != nil {
+		t.Fatalf("ModulePromptFS() error = %v, want nil", err)
+	}
+
+	tests := map[string]string{
+		"assets/prompts/dnd.test/dnd.test.yaml":            "id: dnd.test",
+		"assets/prompts/dnd.test/task.md":                  "task",
+		"assets/prompts/dnd.test/common-dnd-system.md":     "You work with Dungeons & Dragons gameplay transcripts.",
+		"assets/prompts/dnd.test/common-dnd-transcript.md": "{{ input \"transcript\" }}",
+		"assets/prompts/dnd.test/common-dnd-references.md": "Roster reference:",
+	}
+	for path, want := range tests {
+		data, err := fs.ReadFile(fsys, path)
+		if err != nil {
+			t.Fatalf("ReadFile(%q) error = %v, want nil", path, err)
+		}
+		if !strings.Contains(string(data), want) {
+			t.Fatalf("ReadFile(%q) = %q, want substring %q", path, data, want)
+		}
+	}
+
+	entries, err := fs.ReadDir(fsys, ".")
+	if err != nil {
+		t.Fatalf("ReadDir(.) error = %v, want nil", err)
+	}
+	if len(entries) != 1 || entries[0].Name() != "assets" || !entries[0].IsDir() {
+		t.Fatalf("ReadDir(.) = %#v, want assets directory", entries)
+	}
+}
+
+func TestModulePromptFSRejectsMissingModuleFile(t *testing.T) {
+	_, err := ModulePromptFS("dnd.test", fstest.MapFS{}, []ModulePromptFile{
+		{Name: "task.md", Path: "assets/prompts/task.md"},
+	})
+	if err == nil || !strings.Contains(err.Error(), "read module prompt asset assets/prompts/task.md") {
+		t.Fatalf("ModulePromptFS() error = %v, want missing module asset context", err)
+	}
+}
+
+func TestModulePromptFSRejectsMissingSharedFile(t *testing.T) {
+	_, err := modulePromptFS("dnd.test", fstest.MapFS{
+		"assets/prompts/task.md": {Data: []byte("task")},
+	}, []ModulePromptFile{
+		{Name: "task.md", Path: "assets/prompts/task.md"},
+	}, fstest.MapFS{})
+	if err == nil || !strings.Contains(err.Error(), "read shared prompt asset common-dnd-system.md") {
+		t.Fatalf("modulePromptFS() error = %v, want missing shared asset context", err)
+	}
+}
+
+func TestModulePromptFSRejectsNestedVirtualFileName(t *testing.T) {
+	_, err := ModulePromptFS("dnd.test", fstest.MapFS{
+		"assets/prompts/task.md": {Data: []byte("task")},
+	}, []ModulePromptFile{
+		{Name: "nested/task.md", Path: "assets/prompts/task.md"},
+	})
+	if err == nil || !strings.Contains(err.Error(), "must not contain path separators") {
+		t.Fatalf("ModulePromptFS() error = %v, want nested file name error", err)
+	}
+}