Assert: Report RegExp/Error as strings from rejects()/throws()

Report the `actual` (Error object) as a string.
And report an `expected` RegExp or Error object also in its
string form.

Currently, they were reported as their objects, which in the
generic js-reporters module was just printed as an empty object
without any properties because instances of RegExp and instances
of Error both have no own properties that are enumerable.

Fixes #1333.

src/assert.js

@@ -286,12 +286,14 @@ class Assert {
 			// We don't want to validate thrown error
 			if ( !expected ) {
 				result = true;
-				expected = null;
 
 			// Expected is a regexp
 			} else if ( expectedType === "regexp" ) {
 				result = expected.test( errorString( actual ) );
 
+				// Log the string form the regexp
+				expected = String( expected );
+
 			// Expected is a constructor, maybe an Error constructor
 			} else if ( expectedType === "function" && actual instanceof expected ) {
 				result = true;
@@ -302,6 +304,9 @@ class Assert {
 					actual.name === expected.name &&
 					actual.message === expected.message;
 
+				// Log the string form the Error object
+				expected = errorString( expected );
+
 			// Expected is a validation function which returns true if validation passed
 			} else if ( expectedType === "function" && expected.call( {}, actual ) === true ) {
 				expected = null;
@@ -311,7 +316,7 @@ class Assert {
 
 		currentTest.assert.pushResult( {
 			result,
-			actual,
+			actual: errorString( actual ),
 			expected,
 			message
 		} );
@@ -378,12 +383,14 @@ class Assert {
 				// We don't want to validate
 				if ( expected === undefined ) {
 					result = true;
-					expected = actual;
 
 					// Expected is a regexp
 				} else if ( expectedType === "regexp" ) {
 					result = expected.test( errorString( actual ) );
 
+					// Log the string form the regexp
+					expected = String( expected );
+
 					// Expected is a constructor, maybe an Error constructor
 				} else if ( expectedType === "function" && actual instanceof expected ) {
 					result = true;
@@ -394,6 +401,9 @@ class Assert {
 						actual.name === expected.name &&
 						actual.message === expected.message;
 
+					// Log the string form the Error object
+					expected = errorString( expected );
+
 					// Expected is a validation function which returns true if validation passed
 				} else {
 					if ( expectedType === "function" ) {
@@ -412,7 +422,7 @@ class Assert {
 
 				currentTest.assert.pushResult( {
 					result,
-					actual,
+					actual: errorString( actual ),
 					expected,
 					message
 				} );

test/cli/fixtures/expected/tap-outputs.js

@@ -54,12 +54,12 @@ ok 2 Second > 1
 
 	"qunit fail/throws-match.js":
 `TAP version 13
-not ok 1 global failure
+not ok 1 Throws match > bad
   ---
   message: "match error"
   severity: failed
-  actual: {}
-  expected: {}
+  actual: "Error: Match me with a pattern"
+  expected: "/incorrect pattern/"
   stack: .*
   ...
 1..1