Adding test for edge cases of RestUtils.decodeQueryString()

When writing tests for the fix of decodeQueryString() to
handle gracefully edge cases like:

    &a
    &a&b

it arises the question of what behavior is desirable
for these pathological cases (vs the regular p=v pairs).
This change just skips them which is consonant
to the preexisting code.

To be thorough, we add tests for a bunch of edge cases, like:

    QUERY           PARSED PARAMS

    ?               {}
    ?&              {}
    ?=              { "": "" }
    ?a              {}
    ?p=v&a          { "p": "v" }
    ?p=v&a&p1=v1    { "p": "v", "p1": "v1" }
    ?a&b            {}

Author: Adriano Ferreira

modules/elasticsearch/src/test/java/org/elasticsearch/rest/util/RestUtilsTests.java

@@ -60,4 +60,63 @@ public void testDecodeQueryString() {
         RestUtils.decodeQueryString(uri, -1, params);
         assertThat(params.size(), equalTo(0));
     }
+
+    @Test
+    public void testDecodeQueryStringEdgeCases() {
+        Map<String, String> params = newHashMap();
+
+        String uri = "something?";
+        RestUtils.decodeQueryString(uri, uri.indexOf('?') + 1, params);
+        assertThat(params.size(), equalTo(0));
+
+        params.clear();
+        uri = "something?&";
+        RestUtils.decodeQueryString(uri, uri.indexOf('?') + 1, params);
+        assertThat(params.size(), equalTo(0));
+
+        params.clear();
+        uri = "something?p=v&&p1=v1";
+        RestUtils.decodeQueryString(uri, uri.indexOf('?') + 1, params);
+        assertThat(params.size(), equalTo(2));
+        assertThat(params.get("p"), equalTo("v"));
+        assertThat(params.get("p1"), equalTo("v1"));
+
+        params.clear();
+        uri = "something?=";
+        RestUtils.decodeQueryString(uri, uri.indexOf('?') + 1, params);
+        assertThat(params.size(), equalTo(1));
+        assertThat(params.get(""), equalTo(""));
+
+        params.clear();
+        uri = "something?&=";
+        RestUtils.decodeQueryString(uri, uri.indexOf('?') + 1, params);
+        assertThat(params.size(), equalTo(1));
+        assertThat(params.get(""), equalTo(""));
+
+        params.clear();
+        uri = "something?a";
+        RestUtils.decodeQueryString(uri, uri.indexOf('?') + 1, params);
+        assertThat(params.size(), equalTo(0));
+
+        params.clear();
+        uri = "something?p=v&a";
+        RestUtils.decodeQueryString(uri, uri.indexOf('?') + 1, params);
+        assertThat(params.size(), equalTo(1));
+        assertThat(params.get("p"), equalTo("v"));
+
+        params.clear();
+        uri = "something?p=v&a&p1=v1";
+        RestUtils.decodeQueryString(uri, uri.indexOf('?') + 1, params);
+        assertThat(params.size(), equalTo(2));
+        assertThat(params.get("p"), equalTo("v"));
+        assertThat(params.get("p1"), equalTo("v1"));
+
+        params.clear();
+        uri = "something?p=v&a&b&p1=v1";
+        RestUtils.decodeQueryString(uri, uri.indexOf('?') + 1, params);
+        assertThat(params.size(), equalTo(2));
+        assertThat(params.get("p"), equalTo("v"));
+        assertThat(params.get("p1"), equalTo("v1"));
+    }
+
 }