diff --git a/lib/rule-tester/rule-tester.js b/lib/rule-tester/rule-tester.js
index 2ac26534fcc..5180f87a316 100644
--- a/lib/rule-tester/rule-tester.js
+++ b/lib/rule-tester/rule-tester.js
@@ -119,6 +119,32 @@ const RuleTesterParameters = [
     "output"
 ];
 
+/*
+ * All allowed property names in error objects.
+ */
+const errorObjectParameters = new Set([
+    "message",
+    "messageId",
+    "data",
+    "type",
+    "line",
+    "column",
+    "endLine",
+    "endColumn",
+    "suggestions"
+]);
+const friendlyErrorObjectParameterList = `[${[...errorObjectParameters].map(key => `'${key}'`).join(", ")}]`;
+
+/*
+ * All allowed property names in suggestion objects.
+ */
+const suggestionObjectParameters = new Set([
+    "desc",
+    "messageId",
+    "output"
+]);
+const friendlySuggestionObjectParameterList = `[${[...suggestionObjectParameters].map(key => `'${key}'`).join(", ")}]`;
+
 const hasOwnProperty = Function.call.bind(Object.hasOwnProperty);
 
 /**
@@ -573,13 +599,21 @@ class RuleTester {
 
                         // Just an error message.
                         assertMessageMatches(message.message, error);
-                    } else if (typeof error === "object") {
+                    } else if (typeof error === "object" && error !== null) {
 
                         /*
                          * Error object.
                          * This may have a message, messageId, data, node type, line, and/or
                          * column.
                          */
+
+                        Object.keys(error).forEach(propertyName => {
+                            assert.ok(
+                                errorObjectParameters.has(propertyName),
+                                `Invalid error property name '${propertyName}'. Expected one of ${friendlyErrorObjectParameterList}.`
+                            );
+                        });
+
                         if (hasOwnProperty(error, "message")) {
                             assert.ok(!hasOwnProperty(error, "messageId"), "Error should not specify both 'message' and a 'messageId'.");
                             assert.ok(!hasOwnProperty(error, "data"), "Error should not specify both 'data' and 'message'.");
@@ -654,6 +688,17 @@ class RuleTester {
                                 assert.strictEqual(message.suggestions.length, error.suggestions.length, `Error should have ${error.suggestions.length} suggestions. Instead found ${message.suggestions.length} suggestions`);
 
                                 error.suggestions.forEach((expectedSuggestion, index) => {
+                                    assert.ok(
+                                        typeof expectedSuggestion === "object" && expectedSuggestion !== null,
+                                        "Test suggestion in 'suggestions' array must be an object."
+                                    );
+                                    Object.keys(expectedSuggestion).forEach(propertyName => {
+                                        assert.ok(
+                                            suggestionObjectParameters.has(propertyName),
+                                            `Invalid suggestion property name '${propertyName}'. Expected one of ${friendlySuggestionObjectParameterList}.`
+                                        );
+                                    });
+
                                     const actualSuggestion = message.suggestions[index];
 
                                     /**
diff --git a/tests/lib/rule-tester/rule-tester.js b/tests/lib/rule-tester/rule-tester.js
index 7f2b6de67f0..a8bf356fed1 100644
--- a/tests/lib/rule-tester/rule-tester.js
+++ b/tests/lib/rule-tester/rule-tester.js
@@ -182,6 +182,21 @@ describe("RuleTester", () => {
         }, /Error should be a string, object, or RegExp/u);
     });
 
+    it("should throw an error when any of the errors is not a supported type", () => {
+        assert.throws(() => {
+            ruleTester.run("no-var", require("../../fixtures/testers/rule-tester/no-var"), {
+
+                // Only the invalid test matters here
+                valid: [
+                    "bar = baz;"
+                ],
+                invalid: [
+                    { code: "var foo = bar; var baz = quux", errors: [{ type: "VariableDeclaration" }, null] }
+                ]
+            });
+        }, /Error should be a string, object, or RegExp/u);
+    });
+
     it("should throw an error when the error is a string and it does not match error message", () => {
         assert.throws(() => {
             ruleTester.run("no-var", require("../../fixtures/testers/rule-tester/no-var"), {
@@ -232,6 +247,38 @@ describe("RuleTester", () => {
         });
     });
 
+    it("should throw an error when the error is an object with an unknown property name", () => {
+        assert.throws(() => {
+            ruleTester.run("no-var", require("../../fixtures/testers/rule-tester/no-var"), {
+                valid: [
+                    "bar = baz;"
+                ],
+                invalid: [
+                    { code: "var foo = bar;", errors: [{ Message: "Bad var." }] }
+                ]
+            });
+        }, /Invalid error property name 'Message'/u);
+    });
+
+    it("should throw an error when any of the errors is an object with an unknown property name", () => {
+        assert.throws(() => {
+            ruleTester.run("no-var", require("../../fixtures/testers/rule-tester/no-var"), {
+                valid: [
+                    "bar = baz;"
+                ],
+                invalid: [
+                    {
+                        code: "var foo = bar; var baz = quux",
+                        errors: [
+                            { message: "Bad var.", type: "VariableDeclaration" },
+                            { message: "Bad var.", typo: "VariableDeclaration" }
+                        ]
+                    }
+                ]
+            });
+        }, /Invalid error property name 'typo'/u);
+    });
+
     it("should not throw an error when the error is a regex in an object and it matches error message", () => {
         ruleTester.run("no-var", require("../../fixtures/testers/rule-tester/no-var"), {
             valid: [],
@@ -1116,6 +1163,76 @@ describe("RuleTester", () => {
                 });
             }, "Expected the applied suggestion fix to match the test suggestion output");
         });
+
+        it("should fail when specified suggestion isn't an object", () => {
+            assert.throws(() => {
+                ruleTester.run("suggestions-basic", require("../../fixtures/testers/rule-tester/suggestions").basic, {
+                    valid: [],
+                    invalid: [{
+                        code: "var foo;",
+                        errors: [{
+                            suggestions: [null]
+                        }]
+                    }]
+                });
+            }, "Test suggestion in 'suggestions' array must be an object.");
+
+            assert.throws(() => {
+                ruleTester.run("suggestions-messageIds", require("../../fixtures/testers/rule-tester/suggestions").withMessageIds, {
+                    valid: [],
+                    invalid: [{
+                        code: "var foo;",
+                        errors: [{
+                            suggestions: [
+                                {
+                                    messageId: "renameFoo",
+                                    output: "var bar;"
+                                },
+                                "Rename identifier 'foo' to 'baz'"
+                            ]
+                        }]
+                    }]
+                });
+            }, "Test suggestion in 'suggestions' array must be an object.");
+        });
+
+        it("should fail when the suggestion is an object with an unknown property name", () => {
+            assert.throws(() => {
+                ruleTester.run("suggestions-basic", require("../../fixtures/testers/rule-tester/suggestions").basic, {
+                    valid: [
+                        "var boo;"
+                    ],
+                    invalid: [{
+                        code: "var foo;",
+                        errors: [{
+                            suggestions: [{
+                                message: "Rename identifier 'foo' to 'bar'"
+                            }]
+                        }]
+                    }]
+                });
+            }, /Invalid suggestion property name 'message'/u);
+        });
+
+        it("should fail when any of the suggestions is an object with an unknown property name", () => {
+            assert.throws(() => {
+                ruleTester.run("suggestions-messageIds", require("../../fixtures/testers/rule-tester/suggestions").withMessageIds, {
+                    valid: [],
+                    invalid: [{
+                        code: "var foo;",
+                        errors: [{
+                            suggestions: [{
+                                messageId: "renameFoo",
+                                output: "var bar;"
+                            }, {
+                                messageId: "renameFoo",
+                                outpt: "var baz;"
+                            }]
+                        }]
+                    }]
+                });
+            }, /Invalid suggestion property name 'outpt'/u);
+        });
     });
 
     describe("naming test cases", () => {
diff --git a/tests/lib/rules/multiline-comment-style.js b/tests/lib/rules/multiline-comment-style.js
index 456494b7bd5..6c8d4698e06 100644
--- a/tests/lib/rules/multiline-comment-style.js
+++ b/tests/lib/rules/multiline-comment-style.js
@@ -1289,7 +1289,7 @@ ${"                   "}
                 // bar${" "}
             `,
             options: ["separate-lines"],
-            errors: [{ messageid: "expectedlines", line: 2 }]
+            errors: [{ messageId: "expectedLines", line: 2 }]
         },
         {
             code: `
@@ -1303,7 +1303,7 @@ ${"                   "}
                 // bar${" "}
             `,
             options: ["separate-lines"],
-            errors: [{ messageid: "expectedlines", line: 2 }]
+            errors: [{ messageId: "expectedLines", line: 2 }]
         },
         {
             code: `