From 376648d51bc313f041bd40c47edfc75cae8fa45e Mon Sep 17 00:00:00 2001
From: Brandon Mills <mills.brandont@gmail.com>
Date: Fri, 1 Jan 2021 17:30:48 -0500
Subject: [PATCH] WIP New: Add only to RuleTester (refs eslint/rfcs#73)

---
 Makefile.js                    |  2 +-
 lib/rule-tester/rule-tester.js | 56 +++++++++++++++++++++++++++++-----
 2 files changed, 49 insertions(+), 9 deletions(-)

diff --git a/Makefile.js b/Makefile.js
index 840a51a86d7..e32fe62e612 100644
--- a/Makefile.js
+++ b/Makefile.js
@@ -545,7 +545,7 @@ target.mocha = () => {
 
     echo("Running unit tests");
 
-    lastReturn = exec(`${getBinFile("nyc")} -- ${MOCHA} -R progress -t ${MOCHA_TIMEOUT} -c ${TEST_FILES}`);
+    lastReturn = exec(`${getBinFile("nyc")} -- ${MOCHA} --forbid-only -R progress -t ${MOCHA_TIMEOUT} -c ${TEST_FILES}`);
     if (lastReturn.code !== 0) {
         errors++;
     }
diff --git a/lib/rule-tester/rule-tester.js b/lib/rule-tester/rule-tester.js
index 905f3418121..7e788e7ca2a 100644
--- a/lib/rule-tester/rule-tester.js
+++ b/lib/rule-tester/rule-tester.js
@@ -120,7 +120,8 @@ const RuleTesterParameters = [
     "filename",
     "options",
     "errors",
-    "output"
+    "output",
+    "only"
 ];
 
 /*
@@ -281,6 +282,7 @@ function wrapParser(parser) {
 // default separators for testing
 const DESCRIBE = Symbol("describe");
 const IT = Symbol("it");
+const IT_ONLY = Symbol("itOnly");
 
 /**
  * This is `it` default handler if `it` don't exist.
@@ -400,6 +402,38 @@ class RuleTester {
         this[IT] = value;
     }
 
+    static only(item) {
+        if (typeof item === "string") {
+            return { code: item, only: true };
+        }
+
+        return { ...item, only: true };
+    }
+
+    static get itOnly() {
+        if (typeof this[IT_ONLY] === "function") {
+            return this[IT_ONLY];
+        }
+        if (typeof it === "function" && typeof it.only === "function") {
+            return Function.bind.call(it.only, it);
+        }
+
+        if (typeof RuleTester[DESCRIBE] === "function" || typeof RuleTester[IT] === "function") {
+            throw new Error(
+                "Set `RuleTester.itOnly` to use `only` with a custom test framework.\n" +
+                "See https://eslint.org/docs/developer-guide/nodejs-api#customizing-ruletester for more."
+            );
+        }
+        if (typeof it === "function") {
+            throw new Error("The current test framework does not support `only`.");
+        }
+        throw new Error("To use `only`, use RuleTester with a test framework that provides `it.only()` like Mocha.");
+    }
+
+    static set itOnly(value) {
+        this[IT_ONLY] = value;
+    }
+
     /**
      * Define a rule for one particular run of tests.
      * @param {string} name The name of the rule to define.
@@ -881,23 +915,29 @@ class RuleTester {
         RuleTester.describe(ruleName, () => {
             RuleTester.describe("valid", () => {
                 test.valid.forEach(valid => {
-                    RuleTester.it(sanitize(typeof valid === "object" ? valid.code : valid), () => {
-                        testValidTemplate(valid);
-                    });
+                    RuleTester[valid.only ? "itOnly" : "it"](
+                        sanitize(typeof valid === "object" ? valid.code : valid),
+                        () => {
+                            testValidTemplate(valid);
+                        }
+                    );
                 });
             });
 
             RuleTester.describe("invalid", () => {
                 test.invalid.forEach(invalid => {
-                    RuleTester.it(sanitize(invalid.code), () => {
-                        testInvalidTemplate(invalid);
-                    });
+                    RuleTester[invalid.only ? "itOnly" : "it"](
+                        sanitize(invalid.code),
+                        () => {
+                            testInvalidTemplate(invalid);
+                        }
+                    );
                 });
             });
         });
     }
 }
 
-RuleTester[DESCRIBE] = RuleTester[IT] = null;
+RuleTester[DESCRIBE] = RuleTester[IT] = RuleTester[IT_ONLY] = null;
 
 module.exports = RuleTester;