fixup! Assert: Add assert.rejects.

* Add explicit tests for various other invalid types (number, string,
  boolean, array, etc)
* Refactor logic around `expected` being a function in order to properly
  report the difference between invalid expected types and functions
  returning non-true values.

src/assert.js

@@ -313,14 +313,19 @@ class Assert {
 
 		// 'expected' is optional unless doing string comparison
 		if ( objectType( expected ) === "string" ) {
-			if ( message == null ) {
+			if ( message === undefined ) {
 				message = expected;
-				expected = null;
+				expected = undefined;
 			} else {
-				throw new Error(
-					"rejects does not accept a string value for the expected argument.\n" +
-					"Use a non-string object value (e.g. regExp) instead if it's necessary."
-				);
+				message = "rejects does not accept a string value for the expected argument.\n" +
+					"Use a non-string object value (e.g. validator function) instead if necessary.";
+
+				currentTest.assert.pushResult( {
+					result: false,
+					message: message
+				} );
+
+				return;
 			}
 		}
 
@@ -359,8 +364,8 @@ class Assert {
 				if ( actual ) {
 					const expectedType = objectType( expected );
 
-					// We don't want to validate thrown error
-					if ( !expected ) {
+					// We don't want to validate
+					if ( expected === undefined ) {
 						result = true;
 						expected = null;
 
@@ -379,15 +384,22 @@ class Assert {
 							actual.message === expected.message;
 
 						// Expected is a validation function which returns true if validation passed
-					} else if (
-						expectedType === "function" &&
-						expected.call( {}, actual ) === true
-					) {
-						expected = null;
-						result = true;
+					} else {
+						if ( expectedType === "function" ) {
+							result = expected.call( {}, actual ) === true;
+							expected = null;
+
+							// Expected is some other invalid type
+						} else {
+							result = false;
+							message = "invalid expected value provided to `assert.rejects` " +
+								"callback in \"" + currentTest.testName + "\": " +
+								expectedType + ".";
+						}
 					}
 				}
 
+
 				currentTest.assert.pushResult( {
 					result,
 					actual,

test/main/assert.js

@@ -300,6 +300,7 @@ QUnit.test( "rejects", function( assert ) {
 	const rejectsReturnValue = assert.rejects(
 		buildMockPromise( "my error" )
 	);
+
 	assert.equal(
 		typeof rejectsReturnValue.then,
 		"function",
@@ -555,6 +556,30 @@ QUnit.test( "rejects", function( assert ) {
 	);
 
 	assert.rejects( null );
+
+	assert.rejects(
+		buildMockPromise( "foo" ),
+		2,
+		"rejects fails when provided a number"
+	);
+
+	assert.rejects(
+		buildMockPromise( "foo" ),
+		"string matcher",
+		"rejects fails when provided a number"
+	);
+
+	assert.rejects(
+		buildMockPromise( "foo" ),
+		false,
+		"rejects fails when provided a boolean"
+	);
+
+	assert.rejects(
+		buildMockPromise( "foo" ),
+		[],
+		"rejects fails when provided an array"
+	);
 } );
 
 ( function() {