add test for html exports

Do some basic tests of the html export code.

- Make sure that a file was created.
- Make sure that the file can be parsed by an xml parser without error.
- Make sure that the document tag is "html".

app/src/androidTest/java/com/beemdevelopment/aegis/BackupExportTest.java

@@ -61,13 +61,20 @@
 import org.junit.rules.RuleChain;
 import org.junit.rules.TestRule;
 import org.junit.runner.RunWith;
+import org.xmlpull.v1.XmlPullParser;
+import org.xmlpull.v1.XmlPullParserException;
+import org.xmlpull.v1.XmlPullParserFactory;
 
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.Reader;
+import java.nio.charset.StandardCharsets;
 import java.util.Collection;
 import java.util.List;
+import java.util.Locale;
 
 import javax.crypto.Cipher;
 import javax.crypto.SecretKey;
@@ -183,7 +190,9 @@ public void testPlainVaultExportHtml() {
         onView(withText(R.string.export_format_html)).inRoot(RootMatchers.isPlatformPopup()).perform(click());
         onView(withId(android.R.id.button1)).perform(click());
         onView(withId(R.id.checkbox_accept)).perform(click());
-        doExport();
+        File file = doExport();
+
+        checkHtmlExport(file);
     }
 
     @Test
@@ -196,7 +205,9 @@ public void testEncryptedVaultExportHtml() {
         onView(withText(R.string.export_format_html)).inRoot(RootMatchers.isPlatformPopup()).perform(click());
         onView(withId(android.R.id.button1)).perform(click());
         onView(withId(R.id.checkbox_accept)).perform(click());
-        doExport();
+        File file = doExport();
+
+        checkHtmlExport(file);
     }
 
     @Test
@@ -380,6 +391,26 @@ private void readTxtExport(File file) {
         checkReadEntries(entries);
     }
 
+    private void checkHtmlExport(File file) {
+        try (InputStream inStream = new FileInputStream(file)) {
+            Reader inReader = new InputStreamReader(inStream, StandardCharsets.UTF_8);
+            XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
+            XmlPullParser parser = factory.newPullParser();
+            parser.setInput(inReader);
+            while (parser.getEventType() != XmlPullParser.START_TAG) {
+                parser.next();
+            }
+            if (!parser.getName().toLowerCase(Locale.ROOT).equals("html")) {
+                throw new RuntimeException("not an html document!");
+            }
+            while (parser.getEventType() != XmlPullParser.END_DOCUMENT) {
+                parser.next();
+            }
+        } catch (IOException | XmlPullParserException e) {
+            throw new RuntimeException("Unable to read html export file", e);
+        }
+    }
+
     private void checkReadEntries(Collection<VaultEntry> entries) {
         List<VaultEntry> vectors = VaultEntries.get();
         assertEquals(vectors.size(), entries.size());