NoClassDefFoundError when running `mvn surefire:test` in docker image of hadoop trunk

[Xudong SUN <xu...@gmail.com>]

Hello everyone,

I want to submit some patch to hadoop-hdfs so I am trying to run `mvn test`
for hadoop trunk to test my patch. But I met some problem like
```
[ERROR] Failed to execute goal
org.apache.maven.plugins:maven-surefire-plugin:3.0.0-M1:test (default-cli)
on project hadoop-hdfs: Execution default-cli of goal
org.apache.maven.plugins:maven-surefire-plugin:3.0.0-M1:test failed:
java.lang.NoClassDefFoundError:
org/apache/hadoop/fs/contract/AbstractContractUnbufferTest:
org.apache.hadoop.fs.contract.AbstractContractUnbufferTest -> [Help 1]
```
when running tests under hadoop-hdfs-project.

This is what I did:
1. git clone hadoop trunk (839e607)
2. install and start docker
3. run start-build-env.sh
4. run `mvn package` for the whole hadoop and `mvn install` for
hadoop-maven-plugins
5. run `mvn surefire:test` under hadoop-hdfs-project
then `mvn surefire:test` fails with the error message:
```
[ERROR] Failed to execute goal
org.apache.maven.plugins:maven-surefire-plugin:3.0.0-M1:test (default-cli)
on project hadoop-hdfs: Execution default-cli of goal
org.apache.maven.plugins:maven-surefire-plugin:3.0.0-M1:test failed:
java.lang.NoClassDefFoundError:
org/apache/hadoop/fs/contract/AbstractContractUnbufferTest:
org.apache.hadoop.fs.contract.AbstractContractUnbufferTest -> [Help 1]
```
I googled a lot but didn't find any answer for this error.

Here is my question:
How can I successfully run tests in docker image for hadoop trunk? Is there
any important step I missed before running tests?

Thank you a lot!
Best,
Xudong