Github user lfrancke commented on a diff in the pull request:
https://github.com/apache/nifi/pull/2872#discussion_r201489283
--- Diff:
nifi-testharness/src/main/java/org/apache/nifi/testharness/TestNiFiInstance.java
---
@@ -0,0 +1,485 @@
+/*
+ * 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.nifi.testharness;
+
+import org.apache.nifi.testharness.api.FlowFileEditorCallback;
+import org.apache.nifi.EmbeddedNiFi;
+import org.apache.nifi.testharness.util.FileUtils;
+import org.apache.nifi.testharness.util.NiFiCoreLibClassLoader;
+import org.apache.nifi.testharness.util.XmlUtils;
+import org.apache.nifi.testharness.util.Zip;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Objects;
+import java.util.Set;
+import java.util.zip.ZipEntry;
+
+/**
+ * <p>
+ * An API wrapper of a "test" NiFi instance to which a flow definition is
installed for testing.</p>
+ *
+ * <p>
+ * Due to NiFi design restrictions, {@code TestNiFiInstance} has to take
<i>full command</i>
+ * of the current working directory: it installs a full NiFi installation
to there. To ensure
+ * this is desired, <strong>it will only run if the current directory is
called
+ * "nifi_testharness_nifi_home"</strong>. As such the JVM process has to
be started inside a directory
+ * called "nifi_testharness_nifi_home" so that the following is true:
+ *
+ * <pre><tt>
+ * new
File(System.getProperty("user.dir")).getName().equals("nifi_testharness_nifi_home")
+ * </tt></pre>
+ * </p>
+ *
+ * <p>
+ * Before {@code TestNiFiInstance} can be used, it has to be configured
via its builder
+ * interface:
+ * <ul>
+ * <li>
+ * {@link Builder#setFlowXmlToInstallForTesting(File)} specifies the
location of the NiFi binary
+ * distribution ZIP file to be used.
+ * </li>
+ * <li>
+ * {@link Builder#setFlowXmlToInstallForTesting(File)} specifies the
location of the NiFi flow
+ * to install.
+ * </li>
+ * <li>
+ * {@link
Builder#modifyFlowXmlBeforeInstalling(FlowFileEditorCallback)} allows on-the-fly
+ * changes to be performed to the Flow file before it is actually
installed.
+ * </li>
+ * </ul>
+ *
+ * <h5>Sample</h5>
+ * <pre><tt>
+ * TestNiFiInstance testNiFiInstance = TestNiFiInstance.builder()
+ * .setNiFiBinaryDistributionZip(YourConstants.NIFI_ZIP_FILE)
+ * .setFlowXmlToInstallForTesting(YourConstants.FLOW_XML_FILE)
+ *
.modifyFlowXmlBeforeInstalling(YourConstants.FLOW_FILE_CHANGES_FOR_TESTS)
+ * .build();
+ * </tt></pre>
+ *
+ * </p>
+ *
+ * <p>
+ * If the current working directory is called
"nifi_testharness_nifi_home", the caller can
+ * {@link #install()} this {@code TestNiFiInstance}, which will
+ * <ol>
+ * <li>
+ * (as a first cleanup step) erase all content of the current working
directory.
+ * (NOTE: this potentially destructive operation is the reason why we
have the
+ * "nifi_testharness_nifi_home" directory name guard in place!)
+ * </li>
+ * <li>
+ * Extracts the contents of the NiFi binary distribution ZIP file
specified in
+ * the configuration to a to a temporary directory.
+ * <li>
+ * Symlinks all files from the temporary directory to the current
working
+ * directory, causing the to hold a fully functional
+ * NiFi installation.
+ * </li>
+ * <li>
+ * Installs the flow definition files(s) to the NiFi instance
specified in
+ * the configuration.
+ * </li>
+ * </ol>
+ * </p>
+ *
+ * <p>
+ *
+ * The caller then can proceed to {@link #start()}} this {@code
TestNiFiInstance},
+ * which will bootstrap the NiFi engine, which in turn will pick up and
start processing
+ * the flow definition supplied by the caller in the configuration.
+ * </p>
+ *
+ * <p>
+ * Once the previous step is done, the caller can perform asserts
regarding the observed behaviour
+ * of the NiFi flow, just like one would do it with standard Java test
cases.
+ * </p>
+ *
+ * <p>
+ * To perform a clean shutdown of the hosted NiFi instance, the caller is
required to call
+ * {@link #stopAndCleanup()}, which will shut down NiFi and remove all
temporary files, including
+ * the symlinks created int current working directory.
+ * </p>
+ *
+ *
+ * <h4>NOTES</h4>
+ * <ul>
+ * <li>
+ * {@code TestNiFiInstance} is NOT thread safe: if more than one
thread uses it,
+ * external synchronisation is required.
+ * </li>
+ * <li>
+ * Only one {@code TestNiFiInstance} can be started in the same
"nifi_testharness_nifi_home"
+ * directory at the same time.
+ * </li>
+ * <li>
+ * Currently, due to NiFi limitations, one {@TestNiFiInstance} can be
started per JVM process.
--- End diff --
wrong javadoc tag
missing "code"
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