Add README and fix test

Author: zoewangg

migration-tool/README.md

@@ -0,0 +1,37 @@
+# AWS SDK for Java v2 Migration Tool
+
+## Description
+This is a migration tool to automate migration from AWS SDK for Java v1 to AWS SDK for Java v2. 
+It uses [OpenRewrite][open-rewrite].
+
+## Usage
+
+You can use [OpenRewrite Maven plugin][open-rewrite-plugin] to start the migration. See [Running OpenRewrite Recipes][open-rewrite-usage] for more information.
+To get started, you can either perform a dry run or run directly.
+
+- Dry Run 
+
+With this mode, it generates diff logs in the console as well as diff file in the `target` folder.
+Note that you need to replace `{sdkversion}` with the actual SDK version. See [Maven Central][maven-central] to 
+find the latest version.
+
+```
+mvn org.openrewrite.maven:rewrite-maven-plugin:dryRun \
+  -Drewrite.recipeArtifactCoordinates=software.amazon.awssdk:migration-tool:{sdkversion}
+  -Drewrite.activeRecipes=software.amazon.awssdk.UpgradeJavaSdk2
+```
+
+- Run
+
+With this mode, it runs the SDK recipes and applies the changes locally.
+
+```
+mvn org.openrewrite.maven:rewrite-maven-plugin:run \
+  -Drewrite.recipeArtifactCoordinates=software.amazon.awssdk:migration-tool:{sdkversion}
+  -Drewrite.activeRecipes=software.amazon.awssdk.UpgradeJavaSdk2
+```
+
+[open-rewrite]: https://docs.openrewrite.org/
+[open-rewrite-usage]: https://docs.openrewrite.org/running-recipes
+[open-rewrite-plugin]: https://docs.openrewrite.org/reference/rewrite-maven-plugin
+[maven-central]: https://central.sonatype.com/artifact/software.amazon.awssdk/migration-tool

test/migration-tool-tests/src/test/resources/run-test

@@ -22,7 +22,7 @@ def run_test(version):
         shutil.rmtree(TARGET_DIR)
     copy_directory(BEFORE_DIR, TARGET_DIR)
 
-    subprocess.run(["mvn", "org.openrewrite.maven:rewrite-maven-plugin:run",
+    subprocess.run(["mvn", "org.openrewrite.maven:rewrite-maven-plugin:5.21.0:run",
                     "-Drewrite.recipeArtifactCoordinates=software.amazon.awssdk:migration-tool:"+ version,
                     "-Drewrite.activeRecipes=software.amazon.awssdk.UpgradeJavaSdk2"], cwd=TARGET_DIR)
     shutil.rmtree(os.path.join(TARGET_DIR, "target"))