Http image tag extractor using regular expression

HttpImageTagExtractor.java

public class HttpImageTagExtractor {
    public static List<String> extract(String text) {
        //regular expression for extract image tag
        Pattern pattern = Pattern.compile("<img[^>]*src=[\"']?([^>\"']+)[\"']?[^>]*>");
        Matcher matcher = pattern.matcher(text);

        List<String> lists = new ArrayList<>();
        while(matcher.find()) {
            lists.add(matcher.group(1));
        }
        return lists;
    }
}

Junit test code

public class HttpImageTagExtractorTest {
    @Test
    public void shouldReturn0() {
        String text = "<div style=\"text-align:center;\"></div>";
        assertThat(HttpImageTagExtractor.extract(text).size(), is(0));
    }

    @Test
    public void shouldReturn1() {
        String text = "<div style=\"text-align:center;\"><img src=\"img1\"></div>";
        assertThat(HttpImageTagExtractor.extract(text).size(), is(1));
    }

    @Test
    public void shouldReturn2() {
        String text = "<div style=\"text-align:center;\"><img src=\"img2\"><br><img src=\"img1\"></div>";
        assertThat(HttpImageTagExtractor.extract(text).size(), is(2));
    }

    @Test
    public void shouldReturn10() {
        String text = "<div><img src=\"img1\"><img src=\"img2\"><img src=\"img3\"><img src=\"img4\"><img src=\"img5\"><img src=\"img6\"><img src=\"img7\"><img src=\"img8\"><img src=\"img9\"><img src=\"img10\"></div>";
        assertThat(HttpImageTagExtractor.extract(text).size(), is(10));
        assertThat(HttpImageTagExtractor.extract(text).get(9), is("img10"));
    }
}