fix: set configFile to false by default

Author: Kent C. Dodds

README.md

@@ -339,6 +339,7 @@ pluginTester({
     parserOpts: {},
     generatorOpts: {},
     babelrc: false,
+    configFile: false,
   },
   snapshot: false, // use jest snapshots (only works with jest)
 

src/__mocks__/@babel/core.js

@@ -1,3 +1,6 @@
 import * as babel from '@babel/core'
 
+// doing things this way so we can spyOn babel APIs
+// and without this we were getting errors:
+// TypeError: Cannot set property transform of #<Object> which has only a getter
 module.exports = {...babel}

src/index.js

@@ -24,6 +24,7 @@ const fullDefaultConfig = {
     parserOpts: {},
     generatorOpts: {},
     babelrc: false,
+    configFile: false,
   },
 }
 
@@ -303,9 +304,11 @@ const createFixtureTests = (fixturesDir, options) => {
         ...rest
       } = options
 
-      const hasBabelrc = ['.babelrc', '.babelrc.js', '.babelrc.cjs'].some(
-        babelrc => fs.existsSync(path.join(fixtureDir, babelrc)),
-      )
+      const hasBabelrc = [
+        '.babelrc',
+        '.babelrc.js',
+        '.babelrc.cjs',
+      ].some(babelrc => fs.existsSync(path.join(fixtureDir, babelrc)))
 
       const {babelOptions} = mergeWith(
         {},