Adds tests for CertificateGenerator class

Signed-off-by: Darshit Chanpura <dchanp@amazon.com>

src/test/java/org/opensearch/security/tools/democonfig/CertificateGeneratorTests.java

@@ -1,3 +1,86 @@
+/*
+ * 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.
+ *
+ * Modifications Copyright OpenSearch Contributors. See
+ * GitHub history for details.
+ */
+
 package org.opensearch.security.tools.democonfig;
 
-public class CertificateGeneratorTests {}
+import java.io.File;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import org.opensearch.security.tools.democonfig.util.NoExitSecurityManager;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.not;
+import static org.opensearch.security.tools.democonfig.Installer.OPENSEARCH_CONF_DIR;
+import static org.opensearch.security.tools.democonfig.util.DemoConfigHelperUtil.createDirectory;
+import static org.opensearch.security.tools.democonfig.util.DemoConfigHelperUtil.deleteDirectoryRecursive;
+import static org.junit.Assert.fail;
+
+public class CertificateGeneratorTests {
+
+    @Before
+    public void setUp() {
+        OPENSEARCH_CONF_DIR = System.getProperty("user.dir") + File.separator + "test-conf";
+        createDirectory(OPENSEARCH_CONF_DIR);
+    }
+
+    @After
+    public void tearDown() {
+        deleteDirectoryRecursive(OPENSEARCH_CONF_DIR);
+    }
+
+    @Test
+    public void testCreateDemoCertificates() {
+        CertificateGenerator certificateGenerator = new CertificateGenerator();
+        Certificates[] certificatesArray = Certificates.values();
+
+        certificateGenerator.createDemoCertificates();
+
+        for (Certificates cert : certificatesArray) {
+            String certFilePath = OPENSEARCH_CONF_DIR + File.separator + cert.getFileName();
+            File certFile = new File(certFilePath);
+            assertThat(certFile.exists(), is(equalTo(true)));
+            assertThat(certFile.canRead(), is(equalTo(true)));
+
+            String fileContents = null;
+            try {
+                fileContents = new String(Files.readAllBytes(Path.of(certFilePath)));
+            } catch (Exception e) {
+                fail("Expected the test to pass.");
+            }
+
+            assertThat(fileContents.isEmpty(), not(true));
+            assertThat(fileContents, containsString("---BEGIN"));
+            assertThat(fileContents, containsString("---END"));
+        }
+    }
+
+    @Test
+    public void testCreateDemoCertificates_invalidPath() {
+        OPENSEARCH_CONF_DIR = "invalidPath";
+        CertificateGenerator certificateGenerator = new CertificateGenerator();
+        try {
+            System.setSecurityManager(new NoExitSecurityManager());
+            certificateGenerator.createDemoCertificates();
+        } catch (SecurityException e) {
+            assertThat(e.getMessage(), equalTo("System.exit(-1) blocked to allow print statement testing."));
+        } finally {
+            System.setSecurityManager(null);
+        }
+    }
+}