Add state migration test

internal/service/rds/instance_migrate_test.go

@@ -62,3 +62,61 @@ func TestInstanceStateUpgradeV0(t *testing.T) {
 		})
 	}
 }
+
+func TestInstanceStateUpgradeV1(t *testing.T) {
+	ctx := acctest.Context(t)
+	t.Parallel()
+
+	testCases := []struct {
+		Description   string
+		InputState    map[string]interface{}
+		ExpectedState map[string]interface{}
+	}{
+		{
+			Description:   "missing state",
+			InputState:    nil,
+			ExpectedState: nil,
+		},
+		{
+			Description: "change id to resource id",
+			InputState: map[string]interface{}{
+				"allocated_storage": 10,
+				"engine":            "mariadb",
+				"id":                "my-test-instance",
+				"identifier":        "my-test-instance",
+				"instance_class":    "db.t2.micro",
+				"password":          "avoid-plaintext-passwords",
+				"resource_id":       "db-cnuap2ilnbmok4eunzklfvwjca",
+				"tags":              map[string]interface{}{"key1": "value1"},
+				"username":          "tfacctest",
+			},
+			ExpectedState: map[string]interface{}{
+				"allocated_storage": 10,
+				"engine":            "mariadb",
+				"id":                "db-cnuap2ilnbmok4eunzklfvwjca",
+				"identifier":        "my-test-instance",
+				"instance_class":    "db.t2.micro",
+				"password":          "avoid-plaintext-passwords",
+				"resource_id":       "db-cnuap2ilnbmok4eunzklfvwjca",
+				"tags":              map[string]interface{}{"key1": "value1"},
+				"username":          "tfacctest",
+			},
+		},
+	}
+
+	for _, testCase := range testCases {
+		testCase := testCase
+		t.Run(testCase.Description, func(t *testing.T) {
+			t.Parallel()
+
+			got, err := tfrds.InstanceStateUpgradeV1(ctx, testCase.InputState, nil)
+			if err != nil {
+				t.Fatalf("error migrating state: %s", err)
+			}
+
+			if !reflect.DeepEqual(testCase.ExpectedState, got) {
+				t.Fatalf("\n\nexpected:\n\n%#v\n\ngot:\n\n%#v\n\n", testCase.ExpectedState, got)
+			}
+		})
+	}
+}