Add test for ContentTypeHelper, fix format parameter handling

 src/main/java/org/keycloak/protocol/cas/utils/ContentTypeHelper.java

@@ -19,7 +19,8 @@
    public MediaType selectResponseType() {
        String format = uriInfo.getQueryParameters().getFirst(CASLoginProtocol.FORMAT_PARAM);
        if (format != null && !format.isEmpty()) {
            request.getMutableHeaders().add(HttpHeaders.ACCEPT, "application/" + format);
            //if parameter is set, it overrides all header values (see spec section 2.5.1)
            request.getMutableHeaders().putSingle(HttpHeaders.ACCEPT, "application/" + format.toLowerCase());
        }
        Variant variant = restRequest.selectVariant(Variant.mediaTypes(MediaType.APPLICATION_XML_TYPE, MediaType.APPLICATION_JSON_TYPE).build());
        return variant == null ? MediaType.APPLICATION_XML_TYPE : variant.getMediaType();

 src/test/java/org/keycloak/protocol/cas/ContentTypeHelperTest.java

New file
@@ -0,0 +1,45 @@
package org.keycloak.protocol.cas;

import org.jboss.resteasy.mock.MockHttpRequest;
import org.jboss.resteasy.mock.MockHttpResponse;
import org.jboss.resteasy.specimpl.RequestImpl;
import org.junit.Test;
import org.keycloak.protocol.cas.utils.ContentTypeHelper;

import javax.ws.rs.core.HttpHeaders;
import javax.ws.rs.core.MediaType;

import static org.junit.Assert.assertEquals;

public class ContentTypeHelperTest {
    @Test
    public void test() throws Exception {
        assertEquals(MediaType.APPLICATION_XML_TYPE, get("http://example.com/", null).selectResponseType());
        assertEquals(MediaType.APPLICATION_JSON_TYPE, get("http://example.com/?format=json", null).selectResponseType());
        assertEquals(MediaType.APPLICATION_XML_TYPE, get("http://example.com/?format=xml", null).selectResponseType());
        assertEquals(MediaType.APPLICATION_JSON_TYPE, get("http://example.com/?format=JSON", null).selectResponseType());
        assertEquals(MediaType.APPLICATION_XML_TYPE, get("http://example.com/?format=XML", null).selectResponseType());

        assertEquals(MediaType.APPLICATION_XML_TYPE, get("http://example.com/", MediaType.APPLICATION_XML).selectResponseType());
        assertEquals(MediaType.APPLICATION_JSON_TYPE, get("http://example.com/?format=json", MediaType.APPLICATION_XML).selectResponseType());
        assertEquals(MediaType.APPLICATION_XML_TYPE, get("http://example.com/?format=xml", MediaType.APPLICATION_XML).selectResponseType());

        assertEquals(MediaType.APPLICATION_JSON_TYPE, get("http://example.com/", MediaType.APPLICATION_JSON).selectResponseType());
        assertEquals(MediaType.APPLICATION_JSON_TYPE, get("http://example.com/?format=json", MediaType.APPLICATION_JSON).selectResponseType());
        assertEquals(MediaType.APPLICATION_XML_TYPE, get("http://example.com/?format=xml", MediaType.APPLICATION_JSON).selectResponseType());

        assertEquals(MediaType.APPLICATION_XML_TYPE, get("http://example.com/", MediaType.TEXT_PLAIN).selectResponseType());
    }

    private ContentTypeHelper get(String uri, String acceptHeader) throws Exception {
        MockHttpRequest req = MockHttpRequest.get(uri);
        MockHttpResponse res = new MockHttpResponse();
        RequestImpl restReq = new RequestImpl(req, res);

        if (acceptHeader != null) {
            req = req.header(HttpHeaders.ACCEPT, acceptHeader);
        }

        return new ContentTypeHelper(req, restReq, req.getUri());
    }
}