Addressed comments

Author: Kim

src/sagemaker/amazon/amazon_estimator.py

@@ -636,9 +636,10 @@ def get_image_uri(region_name, repo_name, repo_version=1):
                 if repo_version == version.split("-")[0]
             ]
             if xgboost_version_matches:
-                # Assumes that XGBOOST_SUPPORTED_VERSION is sorted from oldest version to latest,
-                # and the latest version is at the end of the list.
-                repo_version = xgboost_version_matches[-1]
+                # Assumes that XGBOOST_SUPPORTED_VERSION is sorted from oldest version to latest.
+                # When SageMaker version is not specified, we use the oldest one that matches
+                # XGBoost version for backward compatibility.
+                repo_version = xgboost_version_matches[0]
 
         supported_framework_versions = [
             version

tests/unit/test_amazon_estimator.py

@@ -475,7 +475,7 @@ def test_get_xgboost_image_uri():
     )
     assert (
         get_image_uri(REGION, "xgboost", "0.90")
-        == "246618743249.dkr.ecr.us-west-2.amazonaws.com/sagemaker-xgboost:0.90-2-cpu-py3"
+        == "246618743249.dkr.ecr.us-west-2.amazonaws.com/sagemaker-xgboost:0.90-1-cpu-py3"
     )
     assert (
         get_image_uri(REGION, "xgboost", "1.0-1")
@@ -527,10 +527,8 @@ def test_is_latest_xgboost_version():
     for version in XGBOOST_SUPPORTED_VERSIONS:
         if version != XGBOOST_LATEST_VERSION:
             assert _is_latest_xgboost_version(version) is False
-
-    assert _is_latest_xgboost_version("0.90-1-cpu-py3") is False
-    assert _is_latest_xgboost_version("0.90-2-cpu-py3") is False
-    assert _is_latest_xgboost_version(XGBOOST_LATEST_VERSION) is True
+        else:
+            assert _is_latest_xgboost_version(version) is True
 
 
 def test_get_image_uri_warn(caplog):