Added test for FsStore values clobbering

It was fixed upstream during a rewrite on functions in FsStore.
See my comments on brutella/hap#28.

bridge_test.go

@@ -0,0 +1,87 @@
+package hapz2m
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"sync"
+	"testing"
+)
+
+const ContactSensorTemplate = `
+		{
+        "network_address": %[1]d,
+        "friendly_name": "0x00158d00aabbcc%02[1]d",
+        "ieee_address":  "0x00158d00aabbcc%02[1]d",
+        "interview_completed": true,
+        "interviewing": false,
+		"disabled": false,
+        "supported": true,
+		"definition": {
+			"exposes": [
+                {
+                    "access": 1,
+                    "name": "contact",
+                    "property": "contact",
+                    "type": "binary",
+                    "value_off": "A",
+                    "value_on": "B"
+                }
+				]
+			}
+		}`
+
+func TestBridgePersistState(t *testing.T) {
+	dir, err := os.MkdirTemp("", "hapz2m-bridge*")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dir)
+
+	var m sync.Map
+	ctx := context.Background()
+
+	b := NewBridge(ctx, dir)
+
+	// devices
+	s1 := fmt.Appendf(nil, ContactSensorTemplate, 10)
+	s2 := fmt.Appendf(nil, ContactSensorTemplate, 20)
+
+	err = b.AddDevicesFromJSON(fmt.Appendf(nil, "[%s, %s]", s1, s2))
+	if err != nil {
+		t.Fatalf("cannot add devices: %v", err)
+	}
+
+	// empty state, should have no errors
+	t.Logf("loading from empty db")
+	if err := b.loadZ2MState(&m); err != nil {
+		t.Errorf("empty state load should not error: %v", err)
+	}
+
+	// save 2 devices
+	t.Logf("persisting state")
+	if err := b.saveZ2MState(); err != nil {
+		t.Errorf("can't persist state: %v", err)
+	}
+
+	// re-create with less devices
+	b2 := NewBridge(ctx, dir)
+	b2.AddDevicesFromJSON(fmt.Appendf(nil, "[%s]", s1))
+
+	t.Logf("loading from initial db")
+	if err := b2.loadZ2MState(&m); err != nil {
+		t.Errorf("load err: %v", err)
+	}
+
+	t.Logf("persisting state")
+	if err := b2.saveZ2MState(); err != nil {
+		t.Errorf("can't persist state: %v", err)
+	}
+
+	// reload from smaller-sized state
+	t.Logf("re-loading from db")
+	if err := b2.loadZ2MState(&m); err != nil {
+		t.Errorf("load err: %v", err)
+	}
+
+}