[CI][C++] TestHadoopFileSystem.FileSystemFromUri fails on our nightly hdfs tests

[raulcd]

Describe the bug, including details regarding any error messages, version, and platform.

Nightly HDFS tests have been failing for the last couple of weeks:

• test-conda-python-3.10-hdfs-2.9.2
• test-conda-python-3.10-hdfs-3.2.1

The error failure is the following:

 [ RUN      ] TestHadoopFileSystem.FileSystemFromUri
/arrow/cpp/src/arrow/filesystem/hdfs_test.cc:119: !!! uri = hdfs://impala:8020/?replication=0&user=hdfs
/arrow/cpp/src/arrow/filesystem/hdfs_test.cc:123: Failure
Expected equality of these values:
  path
    Which is: ""
  "/"
[  FAILED  ] TestHadoopFileSystem.FileSystemFromUri (32 ms)

This was introduced on:
https://github.com/apache/arrow/pull/34420/files#diff-fb718c6107b7bbdeac010067dd0633e0eb3bad5ea054013ffc3bd19652748362

I've been able to fix the build locally by applying this patch to modify the assert on the test:

diff --git a/cpp/src/arrow/filesystem/hdfs_test.cc b/cpp/src/arrow/filesystem/hdfs_test.cc
index 7ad9e6c..5c692ec 100644
--- a/cpp/src/arrow/filesystem/hdfs_test.cc
+++ b/cpp/src/arrow/filesystem/hdfs_test.cc
@@ -120,7 +120,7 @@ class TestHadoopFileSystem : public ::testing::Test, public HadoopFileSystemTest
     ASSERT_OK_AND_ASSIGN(uri_fs, FileSystemFromUri(ss.str(), &path));
     ASSERT_EQ(path, "/");
     ASSERT_OK_AND_ASSIGN(path, uri_fs->PathFromUri(ss.str()));
-    ASSERT_EQ(path, "/");
+    ASSERT_EQ(path, "");
 
     // Sanity check
     ASSERT_OK(uri_fs->CreateDir("AB"));

but I am unsure whether this is the expected behavior or there is an underlying issue.

Component(s)

C++, Continuous Integration

[raulcd]

@westonpace do you think the assert should be modified here or there's something else to be done?

[westonpace]

No, we shouldn't fix the assert. The HDFS filesystem should be returning / in this case (we trim the trailing slash but not if the entire path is /). I can put a fix together.