[prism] add a testcase for correctly binding masgns (#775)

Author: froydnj

fixtures/small/multi_variable_binding_actual.rb

@@ -0,0 +1,9 @@
+def foo
+  some, method = self.method()
+  some, method = self.field.method
+end
+
+def bar
+  (other, method) = self.method()
+  (other, method) = self.field.method
+end

fixtures/small/multi_variable_binding_expected.rb

@@ -0,0 +1,9 @@
+def foo
+  some, method = self.method()
+  some, method = self.field.method
+end
+
+def bar
+  (other, method) = self.method()
+  (other, method) = self.field.method
+end

tests/fixtures_test.rs

@@ -15,6 +15,7 @@ const DISABLED_RIPPER_TESTS: &[&'static str] = &[
     // https://github.com/fables-tales/rubyfmt/issues/474
     "small_args_forwarding_additional_args",
     "small_alias_global_var",
+    "small_multi_variable_binding",
 ];
 
 fn main() -> io::Result<()> {