Check if ok when casting Scan src to string

Author: theFong

amount.go

@@ -360,7 +360,10 @@ func (a Amount) Value() (driver.Value, error) {
 // Allows scanning amounts from a PostgreSQL composite type.
 func (a *Amount) Scan(src interface{}) error {
 	// Wire format: "(9.99,USD)".
-	input := src.(string)
+	input, ok := src.(string)
+	if !ok {
+		return fmt.Errorf("value is not a string: %v", src)
+	}
 	if len(input) == 0 {
 		return nil
 	}

amount_test.go

@@ -930,3 +930,17 @@ func TestAmount_Scan(t *testing.T) {
 		})
 	}
 }
+
+func TestAmount_ScanNonString(t *testing.T) {
+	var a currency.Amount
+	err := a.Scan(123)
+
+	wantError := "value is not a string: 123"
+	errStr := ""
+	if err != nil {
+		errStr = err.Error()
+	}
+	if errStr != wantError {
+		t.Errorf("error: got %v, want %v", errStr, wantError)
+	}
+}