client: add GetStoragePrice for native policy contract

pkg/rpc/client/policy.go

@@ -25,6 +25,14 @@ func (c *Client) GetExecFeeFactor() (int64, error) {
 	return c.invokeNativePolicyMethod("getExecFeeFactor")
 }
 
+// GetStoragePrice invokes `getStoragePrice` method on a native Policy contract.
+func (c *Client) GetStoragePrice() (int64, error) {
+	if !c.initDone {
+		return 0, errNetworkNotInitialized
+	}
+	return c.invokeNativePolicyMethod("getStoragePrice")
+}
+
 // GetMaxNotValidBeforeDelta invokes `getMaxNotValidBeforeDelta` method on a native Notary contract.
 func (c *Client) GetMaxNotValidBeforeDelta() (int64, error) {
 	notaryHash, err := c.GetNativeContractHash(nativenames.Notary)

pkg/rpc/client/rpc_test.go

@@ -428,6 +428,18 @@ var rpcClientTestCases = map[string][]rpcClientTestCase{
 			},
 		},
 	},
+	"getStoragePrice": {
+		{
+			name: "positive",
+			invoke: func(c *Client) (interface{}, error) {
+				return c.GetStoragePrice()
+			},
+			serverResponse: `{"id":1,"jsonrpc":"2.0","result":{"state":"HALT","gasconsumed":"2007390","script":"EMAMDWdldEZlZVBlckJ5dGUMFJphpG7sl7iTBtfOgfFbRiCR0AkyQWJ9W1I=","stack":[{"type":"Integer","value":"100000"}],"tx":null}}`,
+			result: func(c *Client) interface{} {
+				return int64(100000)
+			},
+		},
+	},
 	"getMaxNotValidBeforeDelta": {
 		{
 			name: "positive",