Refactor some tests in HtmlConverterTest

import com.fsck.k9.K9;

import com.fsck.k9.K9.Theme;

import com.fsck.k9.K9RobolectricTestRunner;

import com.fsck.k9.mail.internet.Viewable.Html;

import org.apache.commons.io.IOUtils;

import org.jsoup.Jsoup;

import org.jsoup.nodes.Document;

import org.jsoup.select.Elements;

import org.junit.After;

import org.junit.Before;

import org.junit.Test;

    @Test

    public void wrapMessageContent_addsViewportMetaElement() {

        Document document = Jsoup.parse(HtmlConverter.wrapMessageContent("Some text"));

        Elements metaElements = document.head().getElementsByTag("meta");

        String html = HtmlConverter.wrapMessageContent("Some text");

        assertEquals(1, metaElements.size());

        assertEquals("viewport", metaElements.get(0).attributes().get("name"));

        assertHtmlContainsElement(html, "head > meta[name=viewport]");

    }

    @Test

    public void wrapMessageContent_setsDirToAuto() {

        Document document = Jsoup.parse(HtmlConverter.wrapMessageContent("Some text"));

        String direction = document.getElementsByTag("html").get(0).attributes().get("dir");

        String html = HtmlConverter.wrapMessageContent("Some text");

        assertEquals("auto", direction);

        assertHtmlContainsElement(html, "html[dir=auto]");

    }

    @Test

    public void wrapMessageContent_addsPreCSS() {

        K9.setK9MessageViewThemeSetting(Theme.LIGHT);

        Document document = Jsoup.parse(HtmlConverter.wrapMessageContent("Some text"));

        Elements styleElements = document.head().getElementsByTag("style");

        String html = HtmlConverter.wrapMessageContent("Some text");

        assertEquals(1, styleElements.size());

        assertHtmlContainsElement(html, "head > style");

    }

    @Test

    public void wrapMessageContent_whenDarkMessageViewTheme_addsDarkThemeCSS() {

        K9.setK9MessageViewThemeSetting(Theme.DARK);

        Document document = Jsoup.parse(HtmlConverter.wrapMessageContent("Some text"));

        Elements styleElements = document.head().getElementsByTag("style");

        String html = HtmlConverter.wrapMessageContent("Some text");

        assertEquals(2, styleElements.size());

        assertHtmlContainsElement(html, "head > style", 2);

    }

    @Test

    public void wrapMessageContent_putsMessageContentInBody() {

        String content = "Some text";

        Document document = Jsoup.parse(HtmlConverter.wrapMessageContent(content));

        String actualContent = document.getElementsByTag("body").text();

        assertEquals(content, actualContent);

        String html = HtmlConverter.wrapMessageContent(content);

        assertEquals(content, Jsoup.parse(html).body().text());

    }

    private void assertHtmlContainsElement(String html, String cssQuery) {

        assertHtmlContainsElement(html, cssQuery, 1);

    }

    private void assertHtmlContainsElement(String html, String cssQuery, int numberOfExpectedOccurrences) {

        Document document = Jsoup.parse(html);

        int numberOfFoundElements = document.select(cssQuery).size();

        assertEquals("Expected to find '" + cssQuery + "' " + numberOfExpectedOccurrences + " time(s) in:\n" + html,

                numberOfExpectedOccurrences, numberOfFoundElements);

    }

}