Use at least 2 docs to see deleted docs

Closes #18623

core/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java

@@ -2184,7 +2184,7 @@ public class InternalEngineTests extends ESTestCase {
     }
 
     public void testDocStats() throws IOException {
-        final int numDocs = randomIntBetween(1, 10);
+        final int numDocs = randomIntBetween(2, 10); // at least 2 documents otherwise we don't see any deletes below
         for (int i = 0; i < numDocs; i++) {
             ParsedDocument doc = testParsedDocument(Integer.toString(i), Integer.toString(i), "test", null, -1, -1, testDocument(), new BytesArray("{}"), null);
             Engine.Index firstIndexRequest = new Engine.Index(newUid(Integer.toString(i)), doc, Versions.MATCH_ANY, VersionType.INTERNAL, PRIMARY, System.nanoTime());

core/src/test/java/org/elasticsearch/index/engine/ShadowEngineTests.java

@@ -986,7 +986,7 @@ public class ShadowEngineTests extends ESTestCase {
     }
 
     public void testDocStats() throws IOException {
-        final int numDocs = randomIntBetween(1, 10);
+        final int numDocs = randomIntBetween(2, 10); // at least 2 documents otherwise we don't see any deletes below
         for (int i = 0; i < numDocs; i++) {
             ParsedDocument doc = testParsedDocument(Integer.toString(i), Integer.toString(i), "test", null, -1, -1, testDocument(), new BytesArray("{}"), null);
             Engine.Index firstIndexRequest = new Engine.Index(newUid(Integer.toString(i)), doc, Versions.MATCH_ANY, VersionType.INTERNAL, PRIMARY, System.nanoTime());