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+-   Start Date: 2019-07-16
+-   RFC PR: (leave this empty, to be filled in later)
+-   Authors: Toru Nagashima ([@mysticatea](https://github.com/mysticatea)), Brandon Mills ([@btmills](https://github.com/btmills))
+
+# RuleTester supports processor
+
+## Summary
+
+This RFC makes `RuleTester` class supporting `processor` option.
+
+## Motivation
+
+Currently, we cannot test rules with processors. This is inconvenient for plugin rules which depend on processors. For example, [vue/comment-directive](https://github.com/vuejs/eslint-plugin-vue/blob/6751ff47b4ecd722bc2e2436ce6b34a510f92b07/tests/lib/rules/comment-directive.js) rule could not use `RuleTester` to test. Rules that distinguish between physical and virtual filenames [cannot be tested without processors](https://github.com/eslint/eslint/issues/14800).
+
+## Detailed Design
+
+To add `processor` option and `processorOptions` (see #29) to test cases.
+
+```js
+const { RuleTester } = require("eslint")
+const rule = require("../../../lib/rules/example-rule")
+const exampleProcessor = require("../../../lib/processors/example-processor")
+
+const tester = new RuleTester()
+
+tester.run("example-rule", rule, {
+    valid: [
+        {
+            code: `
+                <script>
+                    console.log("Hello")
+                </script>
+            `,
+            processor: exampleProcessor,
+            processorOptions: {},
+        },
+    ],
+    invalid: [],
+})
+```
+
+### § `processor` option
+
+This is a definition object of a processor that the "[Processors in Plugins](https://eslint.org/docs/developer-guide/working-with-plugins#processors-in-plugins)" section describes.
+
+If a processor is given, the tester passes its `preprocess`, `postprocess`, and optional `supportsAutofix` properties as part of `Linter#verify()`'s `filenameOrOptions` options object.
+
+The tester only applies fixes if the processor also has `supportsAutofix: true`.
+
+### § `processorOptions` option
+
+RFC #29 defines the `processorOptions`, though it has not yet been implemented.
+
+If this option was given along with `processor` option, it will be given to the processor.
+
+## Documentation
+
+The [RuleTester](https://eslint.org/docs/developer-guide/nodejs-api#ruletester) section should describe the new `processor` and, if implemented, `processorOptions` properties.
+
+## Drawbacks
+
+This expands `RuleTester`'s purpose to include testing processor-aware rules.
+Some could see this as out of scope for `RuleTester`.
+
+It adds additional complexity to `RuleTester`, though it is minimal.
+
+This design only supports a single processor.
+
+## Backwards Compatibility Analysis
+
+`RuleTester` currently accepts the `processor` key as a string in valid and invalid test case objects, but it does nothing with that string.
+It throws an error if `processor` is set to any non-string type.
+If someone has set `processor` to a string value in any of their test cases, those tests would throw with this change.
+Because the `processor` key does nothing prior to this change, having it is unlikely, and the fix is easy: deleting the `processor` key leaves the test logically unchanged.
+
+## Alternatives
+
+- To support testing rules that distinguish between physical and virtual filenames, we could instead add a `physicalFilename` option to test cases and modify `Linter` to use that option instead of computing filenames.
+
+## Open Questions
+
+- Does this design need to accept multiple nested processors?
+
+## Help Needed
+
+I can implement this myself.
+
+## Frequently Asked Questions
+
+None yet.
+## Related Discussions
+
+- https://github.com/eslint/rfcs/pull/25#issuecomment-499877621
+- https://github.com/eslint/eslint/issues/14800