fix: add guard for missing assertion invocation (#58)

Author: tinovyatkin

rules/__tests__/prefer-to-be-null.test.js

@@ -18,6 +18,7 @@ ruleTester.run('prefer-to-be-null', rule, {
     'expect("a string").toMatchSnapshot(null);',
     'expect("a string").not.toMatchSnapshot();',
     "expect(something).toEqual('a string');",
+    'expect(null).toBe',
   ],
 
   invalid: [

rules/__tests__/prefer-to-be-undefined.test.js

@@ -15,6 +15,7 @@ ruleTester.run('prefer-to-be-undefined', rule, {
     'expect(something).toEqual(somethingElse)',
     'expect(something).not.toBe(somethingElse)',
     'expect(something).not.toEqual(somethingElse)',
+    'expect(undefined).toBe',
   ],
 
   invalid: [

rules/util.js

@@ -73,9 +73,11 @@ const methodName = node => method(node).name;
 
 const methodName2 = node => method2(node).name;
 
-const argument = node => node.parent.parent.arguments[0];
+const argument = node =>
+  node.parent.parent.arguments && node.parent.parent.arguments[0];
 
-const argument2 = node => node.parent.parent.parent.arguments[0];
+const argument2 = node =>
+  node.parent.parent.parent.arguments && node.parent.parent.parent.arguments[0];
 
 const describeAliases = Object.assign(Object.create(null), {
   describe: true,