Update: added empty error array check for false negative

lib/rule-tester/rule-tester.js

@@ -644,13 +644,22 @@ class RuleTester {
             assert.ok(item.errors || item.errors === 0,
                 `Did not specify errors for an invalid test of ${ruleName}`);
 
+            if (Array.isArray(item.errors) && item.errors.length === 0) {
+                assert.fail("errors array should have at least one element otherwise its a valid case");
+            }
+
             const ruleHasMetaMessages = hasOwnProperty(rule, "meta") && hasOwnProperty(rule.meta, "messages");
             const friendlyIDList = ruleHasMetaMessages ? `[${Object.keys(rule.meta.messages).map(key => `'${key}'`).join(", ")}]` : null;
 
             const result = runRuleForItem(item);
             const messages = result.messages;
 
             if (typeof item.errors === "number") {
+
+                if (item.errors === 0) {
+                    assert.fail("errors of type `number` should not have value `0`");
+                }
+
                 assert.strictEqual(messages.length, item.errors, util.format("Should have %d error%s but had %d: %s",
                     item.errors, item.errors === 1 ? "" : "s", messages.length, util.inspect(messages)));
             } else {

tests/lib/rule-tester/rule-tester.js

@@ -463,6 +463,37 @@ describe("RuleTester", () => {
         }, expectedErrorMessage);
     });
 
+    it("should throw error for empty error array", () => {
+        assert.throws(() => {
+            ruleTester.run("suggestions-messageIds", require("../../fixtures/testers/rule-tester/suggestions").withMessageIds, {
+                valid: [],
+                invalid: [{
+                    code: "var foo;",
+                    errors: []
+                }]
+            });
+        }, /errors array should have at least one element otherwise its a valid case/u);
+    });
+
+    it("should throw error for errors : 0", () => {
+        assert.throws(() => {
+            ruleTester.run(
+                "suggestions-messageIds",
+                require("../../fixtures/testers/rule-tester/suggestions")
+                    .withMessageIds,
+                {
+                    valid: [],
+                    invalid: [
+                        {
+                            code: "var foo;",
+                            errors: 0
+                        }
+                    ]
+                }
+            );
+        }, /errors of type `number` should not have value `0`/u);
+    });
+
     it("should not skip column assertion if column is a falsy value", () => {
         assert.throws(() => {
             ruleTester.run("no-eval", require("../../fixtures/testers/rule-tester/no-eval"), {
@@ -732,7 +763,7 @@ describe("RuleTester", () => {
                 {
                     code: "eval(foo)",
                     parser: require.resolve("esprima"),
-                    errors: [{}]
+                    errors: [{ line: 1 }]
                 }
             ]
         });
@@ -1893,4 +1924,5 @@ describe("RuleTester", () => {
         });
 
     });
+
 });