Add Tests for file package

[joeyyy09]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Following New tests are added to the file package.
TestCreate, TestCopy, TestAppend, TestExists, TestRemove, TestOpen, TestRead, TestWrite, TestMkdirAll

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

NONE

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: joeyyy09
Once this PR has been reviewed and has the lgtm label, please assign wzshiming for approval. For more information see the Kubernetes Code Review Process.

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• OWNERS

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[k8s-ci-robot]

Hi @joeyyy09. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

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[k8s-triage-robot]

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This bot triages PRs according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
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You can:

• Mark this PR as fresh with /remove-lifecycle stale
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/lifecycle stale

[joeyyy09]

/remove-lifecycle stale