Cleanup "when parsed as XML" tests.

Of particular note is the test intended to check that when DOMParser
is available, that it would be used to parse the XML. Actually make
this assertion by checking it was called with the correct arguments.

test/index.spec.js

@@ -750,7 +750,8 @@ describe('unexpected-dom', () => {
 
   describe('when parsed as XML', () => {
     const xmlSrc = '<?xml version="1.0"?><fooBar yes="sir">foo</fooBar>';
-    it('should parse a string as a complete XML document', () => {
+
+    it('should parse a string as a complete XML document (attributes)', () => {
       expect(
         xmlSrc,
         'when parsed as XML',
@@ -763,22 +764,33 @@ describe('unexpected-dom', () => {
       );
     });
 
-    it('should provide the parsed document as the fulfillment value when no assertion is provided', () =>
+    it('should parse a string as a complete XML document (text)', () => {
       expect(
-        '<?xml version="1.0"?><fooBar yes="sir">foo</fooBar>',
-        'parsed as XML'
-      ).then(document => {
+        xmlSrc,
+        'when parsed as XML',
+        'queried for first',
+        'fooBar',
+        'to have text',
+        'foo'
+      );
+    });
+
+    it('should provide the parsed document as the fulfillment value when no assertion is provided', () =>
+      expect(xmlSrc, 'parsed as XML').then(document => {
         expect(document, 'queried for first', 'fooBar', 'to have attributes', {
           yes: 'sir'
         });
       }));
 
     describe('when the DOMParser global is available', () => {
       const OriginalDOMParser = root.DOMParser;
+      let seenDomParserArgs;
 
       beforeEach(() => {
+        seenDomParserArgs = null;
         DOMParser = class DOMParser {
           parseFromString(str) {
+            seenDomParserArgs = [str];
             return typeof jsdom !== 'undefined'
               ? new jsdom.JSDOM(str, { contentType: 'text/xml' }).window
                   .document
@@ -793,13 +805,16 @@ describe('unexpected-dom', () => {
 
       it('should use DOMParser to parse the document', () => {
         expect(
-          xmlSrc,
-          'when parsed as XML',
-          'queried for first',
-          'fooBar',
-          'to have text',
-          'foo'
-        );
+          () =>
+            expect(
+              xmlSrc,
+              'when parsed as XML',
+              expect.it('to be an', 'XMLDocument')
+            ),
+          'to be fulfilled'
+        ).then(() => {
+          expect(seenDomParserArgs, 'to equal', [xmlSrc]);
+        });
       });
     });
   });