Add test for cassandra error

[hlts2]

Description:

I implemented the test for Cassandra's error.

grammar check passed*

Related

https://github.com/vdaas/vald/projects/3#card-50354274

Related Issue:

How Has This Been Tested?:

Environment:

• Go Version: 1.15.2
• Docker Version: 19.03.8
• Kubernetes Version: 1.18.2
• NGT Version: 1.12.1

Types of changes:

• Bug fix [type/bug]
• New feature [type/feature]
• Add tests [type/test]
• Security related changes [type/security]
• Add documents [type/documentation]
• Refactoring [type/refactoring]
• Update dependencies [type/dependency]
• Update benchmarks and performances [type/bench]
• Update CI [type/ci]

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?

Checklist:

• I have read the CONTRIBUTING document.
• I have checked open Pull Requests for the similar feature or fixes?
• I have added tests and benchmarks to cover my changes.
• I have ensured all new and existing tests passed.
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly.

[vdaas-ci]

[CHATOPS:HELP] ChatOps commands.

• 🙆‍♀️ /approve - approve
• 💌 /changelog - add changelog comment
• 🍱 /format - format codes and add licenses
• ✅ /gen-test - generate test codes
• 🏷️ /label - add labels
• ⏪ /rebase - rebase master

[codecov]

Codecov Report

Merging #865 (d0f743a) into master (f72ff79) will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #865      +/-   ##
==========================================
- Coverage   18.85%   18.80%   -0.05%     
==========================================
  Files         423      422       -1     
  Lines       19600    19572      -28     
==========================================
- Hits         3696     3681      -15     
+ Misses      15685    15676       -9     
+ Partials      219      215       -4     

Impacted Files	Coverage Δ
internal/errors/cassandra.go	100.00% <ø> (+100.00%)	⬆️
internal/errors/compressor.go	0.00% <0.00%> (-100.00%)	⬇️
internal/db/storage/blob/s3/s3.go	0.00% <0.00%> (-94.29%)	⬇️
internal/net/http/client/client.go	0.00% <0.00%> (-89.48%)	⬇️
internal/worker/worker.go	83.33% <0.00%> (ø)
internal/net/grpc/client.go	0.00% <0.00%> (ø)
pkg/agent/core/ngt/service/ngt.go	0.00% <0.00%> (ø)
internal/db/storage/blob/s3/option.go	100.00% <0.00%> (ø)
internal/db/storage/blob/s3/reader/option.go	100.00% <0.00%> (ø)
internal/db/storage/blob/s3/writer/option.go	100.00% <0.00%> (ø)
... and 6 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 933cba5...df214aa. Read the comment docs.

[kevindiu]

LGTM

[kevindiu]

LGTM

[vdaas-ci]

[FORMAT] Updating license headers and formatting go codes triggered by vankichi.

[vdaas-ci]

[APPROVED] This PR is approved by vankichi.