diff --git a/solr/CHANGES.txt b/solr/CHANGES.txt
index 4838245e1d2..19f27adf52d 100644
--- a/solr/CHANGES.txt
+++ b/solr/CHANGES.txt
@@ -157,6 +157,8 @@ Other Changes
 
 * SOLR-17142: Fix Gradle build sometimes gives spurious "unreferenced license file" warnings. (Uwe Schindler)
 
+* SOLR-11318: Introduce unit testing for AssertTool. (Eric Pugh, Jason Gerlowski)
+
 ==================  9.7.0 ==================
 New Features
 ---------------------
diff --git a/solr/core/src/test/org/apache/solr/cli/AssertToolTest.java b/solr/core/src/test/org/apache/solr/cli/AssertToolTest.java
new file mode 100644
index 00000000000..87ada1cfdcf
--- /dev/null
+++ b/solr/core/src/test/org/apache/solr/cli/AssertToolTest.java
@@ -0,0 +1,169 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF 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.apache.solr.cli;
+
+import static org.apache.solr.cli.SolrCLI.findTool;
+import static org.apache.solr.cli.SolrCLI.parseCmdLine;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Set;
+import org.apache.commons.cli.CommandLine;
+import org.apache.solr.client.solrj.impl.CloudSolrClient;
+import org.apache.solr.cloud.SolrCloudTestCase;
+import org.apache.solr.common.cloud.ZkStateReader;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class AssertToolTest extends SolrCloudTestCase {
+
+  @BeforeClass
+  public static void setupCluster() throws Exception {
+    configureCluster(1).addConfig("conf", configset("cloud-minimal")).configure();
+  }
+
+  @Test
+  public void raisesExitCode100OnError() throws Exception {
+    assumeTrue(
+        "This test only works with security manager, as it raises an error accessing /tmp",
+        System.getSecurityManager() != null);
+    final String[] args = new String[] {"assert", "--exitcode", "--exists", "/tmp"};
+
+    final int numAssertionsFailed = runAssertToolWithArgs(args);
+
+    assertEquals("Expected AssertTool to raise an error", numAssertionsFailed, 100);
+  }
+
+  @Test
+  public void checksForTheExistenceOfDirectoryThatExists() throws Exception {
+    Path tempDir = Files.createTempDirectory("myTempDir");
+    final String[] args = new String[] {"assert", "--exitcode", "--exists", tempDir.toString()};
+
+    final int numAssertionsFailed = runAssertToolWithArgs(args);
+
+    assertEquals(
+        "Expected AssertTool to pass assertion that directory exists", numAssertionsFailed, 0);
+  }
+
+  @Test
+  public void checksForTheExistenceOfDirectoryThatDoesntExist() throws Exception {
+    // we create a tempdir to avoid the Java Security Manager flagging that we can't access
+    // /foo/bar/baz directly.
+    Path tempDir = Files.createTempDirectory("myTempDir");
+    final String[] args =
+        new String[] {"assert", "--exitcode", "--exists", tempDir.toString() + "/foo/bar/baz"};
+
+    final int numAssertionsFailed = runAssertToolWithArgs(args);
+
+    assertEquals(
+        "Expected AssertTool to fail assertion that directory exists", numAssertionsFailed, 1);
+  }
+
+  @Test
+  public void checksForTheNonExistenceOfDirectoryThatExists() throws Exception {
+    Path tempDir = Files.createTempDirectory("myTempDir");
+    final String[] args = new String[] {"assert", "--exitcode", "--not-exists", tempDir.toString()};
+
+    final int numAssertionsFailed = runAssertToolWithArgs(args);
+
+    assertEquals(
+        "Expected AssertTool to fail assertion that directory doesnt exist",
+        numAssertionsFailed,
+        1);
+  }
+
+  @Test
+  public void checksForTheNonExistenceDirectoryThatDoesntExist() throws Exception {
+    Path tempDir = Files.createTempDirectory("myTempDir");
+    final String[] args =
+        new String[] {"assert", "--exitcode", "--not-exists", tempDir.toString() + "/foo/bar/baz"};
+
+    final int numAssertionsFailed = runAssertToolWithArgs(args);
+
+    assertEquals(
+        "Expected AssertTool to fail assertion that directory doesnt exist",
+        numAssertionsFailed,
+        0);
+  }
+
+  @Test
+  public void checksForThePresenceOfSolrOnCorrectUrl() throws Exception {
+    final String baseUrl = getRealSolrBaseUrl();
+    final String[] args = new String[] {"assert", "--exitcode", "--started", baseUrl};
+
+    final int numAssertionsFailed = runAssertToolWithArgs(args);
+
+    assertEquals(
+        "Expected AssertTool to pass assertion when Solr is running on provided URL",
+        numAssertionsFailed,
+        0);
+  }
+
+  @Test
+  public void checksForThePresenceOfSolrOnIncorrectUrl() throws Exception {
+    final String[] args =
+        new String[] {"assert", "--exitcode", "--started", "http://www.google.com"};
+
+    final int numAssertionsFailed = runAssertToolWithArgs(args);
+
+    assertEquals(
+        "Expected AssertTool to fail assertion when Solr isn't running on provided URL",
+        numAssertionsFailed,
+        1);
+  }
+
+  @Test
+  public void checksForTheAbsenceOfSolrOnCorrectUrl() throws Exception {
+    final String baseUrl = getRealSolrBaseUrl();
+    final String[] args = new String[] {"assert", "--exitcode", "--not-started", baseUrl};
+
+    final int numAssertionsFailed = runAssertToolWithArgs(args);
+
+    assertEquals(
+        "Expected AssertTool to fail assertion when Solr is running on provided URL",
+        numAssertionsFailed,
+        1);
+  }
+
+  @Test
+  public void checksForTheAbsenceOfSolrOnIncorrectUrl() throws Exception {
+    final String[] args =
+        new String[] {"assert", "--exitcode", "--not-started", "http://www.google.com"};
+
+    final int numAssertionsFailed = runAssertToolWithArgs(args);
+
+    assertEquals(
+        "Expected AssertTool to pass assertion when Solr isn't running on provided URL",
+        numAssertionsFailed,
+        0);
+  }
+
+  private int runAssertToolWithArgs(String[] args) throws Exception {
+    Tool tool = findTool(args);
+    assertTrue(tool instanceof AssertTool);
+    final CommandLine cli = parseCmdLine(tool, args);
+    return tool.runTool(cli);
+  }
+
+  private String getRealSolrBaseUrl() {
+    final CloudSolrClient cloudSolrClient = cluster.getSolrClient();
+    final Set<String> liveNodes = cloudSolrClient.getClusterState().getLiveNodes();
+    final String firstLiveNode = liveNodes.iterator().next();
+
+    return ZkStateReader.from(cloudSolrClient).getBaseUrlForNodeName(firstLiveNode);
+  }
+}