service: add some unit test cases

[hijackthe2]

…e.rs, singleton.rs under service/src

1. In blob_cache.rs, two simple lines of code have been added to cover previously missed cases.
2. In block_device.rs, some test cases are added to cover function export(), block_size(), blocks_to_size(), and size_to_blocks().
3. In fs_cache.rs, some test cases are added to cover function try_from() for struct FsCacheMsgOpen and FsCacheMsgRead.
4. In singletion.rs, some test cases are added to cover function initialize_blob_cache() and initialize_fscache_service(). In addition, fscache must be correctly enabled as the device file /dev/cachefiles will used by function initialize_fscache_service().

i#tests: add unit test case for service/src/block_device.rs

Relevant Issue (if applicable)

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Details

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Types of changes

What types of changes does your PullRequest introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

Checklist

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• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[codecov]

Codecov Report

Merging #1455 (62adc28) into master (ac55d7f) will increase coverage by 1.28%.
The diff coverage is 98.71%.

@@            Coverage Diff             @@
##           master    #1455      +/-   ##
==========================================
+ Coverage   44.37%   45.65%   +1.28%     
==========================================
  Files         123      123              
  Lines       38896    39170     +274     
  Branches    38896    39170     +274     
==========================================
+ Hits        17260    17885     +625     
+ Misses      20695    20298     -397     
- Partials      941      987      +46     

Files	Coverage Δ
service/src/blob_cache.rs	82.69% <100.00%> (+4.44%)	⬆️
service/src/fs_cache.rs	29.21% <100.00%> (+20.48%)	⬆️
service/src/singleton.rs	55.26% <100.00%> (+55.26%)	⬆️
service/src/block_device.rs	75.81% <96.99%> (+37.21%)	⬆️

... and 10 files with indirect coverage changes

[adamqqqplay]

Thanks for your contrbution!

Maybe you could tidy up the commit logs, the current commit logs are a bit redundant.
For example: "smoke ci configurations" could change to "ci" or "action".

[hijackthe2]

Thanks for your contrbution!

Maybe you could tidy up the commit logs, the current commit logs are a bit redundant. For example: "smoke ci configurations" could change to "ci" or "action".

Thanks for reply! I have already adjusted the commit information.