Introduce unit tests for ValuesSourceType (#43174)

As the ValuesSourceType evolves, it is important to be
confident that new enum constants do not break
backwards-compatibility on the stream. Having dedicated
unit tests for this class will help be sure of that.

Author: talevy

server/src/test/java/org/elasticsearch/search/aggregations/support/ValuesSourceTypeTests.java

@@ -0,0 +1,69 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.search.aggregations.support;
+
+import org.elasticsearch.common.io.stream.AbstractWriteableEnumTestCase;
+
+import java.io.IOException;
+
+import static org.hamcrest.Matchers.equalTo;
+
+public class ValuesSourceTypeTests extends AbstractWriteableEnumTestCase {
+
+    public ValuesSourceTypeTests() {
+        super(ValuesSourceType::fromStream);
+    }
+
+    @Override
+    public void testValidOrdinals() {
+        assertThat(ValuesSourceType.ANY.ordinal(), equalTo(0));
+        assertThat(ValuesSourceType.NUMERIC.ordinal(), equalTo(1));
+        assertThat(ValuesSourceType.BYTES.ordinal(), equalTo(2));
+        assertThat(ValuesSourceType.GEOPOINT.ordinal(), equalTo(3));
+    }
+
+    @Override
+    public void testFromString() {
+        assertThat(ValuesSourceType.fromString("any"), equalTo(ValuesSourceType.ANY));
+        assertThat(ValuesSourceType.fromString("numeric"), equalTo(ValuesSourceType.NUMERIC));
+        assertThat(ValuesSourceType.fromString("bytes"), equalTo(ValuesSourceType.BYTES));
+        assertThat(ValuesSourceType.fromString("geopoint"), equalTo(ValuesSourceType.GEOPOINT));
+        IllegalArgumentException e = expectThrows(IllegalArgumentException.class, () -> ValuesSourceType.fromString("does_not_exist"));
+        assertThat(e.getMessage(),
+            equalTo("No enum constant org.elasticsearch.search.aggregations.support.ValuesSourceType.DOES_NOT_EXIST"));
+        expectThrows(NullPointerException.class, () -> ValuesSourceType.fromString(null));
+    }
+
+    @Override
+    public void testReadFrom() throws IOException {
+        assertReadFromStream(0, ValuesSourceType.ANY);
+        assertReadFromStream(1, ValuesSourceType.NUMERIC);
+        assertReadFromStream(2, ValuesSourceType.BYTES);
+        assertReadFromStream(3, ValuesSourceType.GEOPOINT);
+    }
+
+    @Override
+    public void testWriteTo() throws IOException {
+        assertWriteToStream(ValuesSourceType.ANY, 0);
+        assertWriteToStream(ValuesSourceType.NUMERIC, 1);
+        assertWriteToStream(ValuesSourceType.BYTES, 2);
+        assertWriteToStream(ValuesSourceType.GEOPOINT, 3);
+    }
+}