Added basic unit tests for the FeatureFlags utility class

Signed-off-by: Kartik Ganesh <[email protected]>

server/src/test/java/org/opensearch/common/util/FeatureFlagTests.java

@@ -0,0 +1,26 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.common.util;
+
+import org.opensearch.test.OpenSearchTestCase;
+
+public class FeatureFlagTests extends OpenSearchTestCase {
+
+    public void testMissingFeatureFlag() {
+        String testFlag = "missingFeatureFlag";
+        assertNull(System.getProperty(testFlag));
+        assertFalse(FeatureFlags.isEnabled(testFlag));
+    }
+
+    public void testNonBooleanFeatureFlag() {
+        String javaVersionProperty = "java.version";
+        assertNotNull(System.getProperty(javaVersionProperty));
+        assertFalse(FeatureFlags.isEnabled(javaVersionProperty));
+    }
+}