fix: support throwing of unusual errors

Adds support for throwing things like `undefined`, functions, etc.

lib/chai/core/assertions.js

@@ -2681,10 +2681,12 @@ function assertThrows (errorLike, errMsgMatcher, msg) {
     errorLike = null;
   }
 
-  var caughtErr;
+  let caughtErr;
+  let errorWasThrown = false;
   try {
     obj();
   } catch (err) {
+    errorWasThrown = true;
     caughtErr = err;
   }
 
@@ -2708,14 +2710,26 @@ function assertThrows (errorLike, errMsgMatcher, msg) {
       errorLikeString = _.checkError.getConstructorName(errorLike);
     }
 
+    let actual = caughtErr;
+    if (caughtErr instanceof Error) {
+      actual = caughtErr.toString();
+    } else if (typeof caughtErr === 'string') {
+      actual = caughtErr;
+    } else if (caughtErr && (typeof caughtErr === 'object' || typeof caughtErr === 'function')) {
+      try {
+        actual = _.checkError.getConstructorName(caughtErr);
+      } catch (_err) {
+        // somehow wasn't a constructor, maybe we got a function thrown
+        // or similar
+      }
+    }
+
     this.assert(
-        caughtErr !== undefined
+      errorWasThrown
       , 'expected #{this} to throw ' + errorLikeString
       , 'expected #{this} to not throw an error but #{act} was thrown'
       , errorLike && errorLike.toString()
-      , (caughtErr instanceof Error ?
-          caughtErr.toString() : (typeof caughtErr === 'string' ? caughtErr : caughtErr &&
-                                  _.checkError.getConstructorName(caughtErr)))
+      , actual
     );
   }
 

lib/chai/utils/index.js

@@ -95,6 +95,12 @@ export {isNaN} from './isNaN.js';
 // getOperator method
 export {getOperator} from './getOperator.js';
 
+/**
+ * Determines if an object is a `RegExp`
+ * This is used since `instanceof` will not work in virtual contexts
+ * @param {*} obj Object to test
+ * @return {boolean}
+ */
 export function isRegExp(obj) {
   return Object.prototype.toString.call(obj) === '[object RegExp]';
 }

test/assert.js

@@ -1635,6 +1635,8 @@ describe('assert', function () {
   });
 
   it('throws / throw / Throw', function() {
+    class CustomError extends Error {}
+
     ['throws', 'throw', 'Throw'].forEach(function (throws) {
       assert[throws](function() { throw new Error('foo'); });
       assert[throws](function() { throw new Error(''); }, '');
@@ -1647,6 +1649,9 @@ describe('assert', function () {
       assert[throws](function() { throw ''; }, '');
       assert[throws](function() { throw ''; }, /^$/);
       assert[throws](function() { throw new Error(''); }, /^$/);
+      assert[throws](function() { throw undefined; });
+      assert[throws](function() { throw new CustomError('foo'); });
+      assert[throws](function() { throw (() => {}); });
 
       var thrownErr = assert[throws](function() { throw new Error('foo'); });
       assert(thrownErr instanceof Error, 'assert.' + throws + ' returns error');