feat(modules): add hello toy module as engine smoke test

internal/modules/hello/hello_test.go

@@ -0,0 +1,57 @@
+package hello
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/MDietermann/ArduinoArchSetup/internal/engine"
+)
+
+func TestHelloFullLifecycle(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "hello.ok")
+	m := Module{Path: path}
+	ctx := context.Background()
+
+	st, err := m.Detect(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if st.(state).Present {
+		t.Fatal("marker should be absent on fresh tmpdir")
+	}
+
+	plan, err := m.Plan(ctx, st)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if plan.IsEmpty() {
+		t.Fatal("plan should have one action")
+	}
+
+	if err := m.Apply(ctx, plan, engine.NewBufferedReporter()); err != nil {
+		t.Fatal(err)
+	}
+	if err := m.Verify(ctx); err != nil {
+		t.Fatal(err)
+	}
+
+	st2, _ := m.Detect(ctx)
+	if !st2.(state).Present {
+		t.Fatal("marker should be present after apply")
+	}
+
+	plan2, _ := m.Plan(ctx, st2)
+	if !plan2.IsEmpty() {
+		t.Fatal("second plan should be empty (idempotent)")
+	}
+
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(data) != markerContent {
+		t.Fatalf("content = %q", data)
+	}
+}