Tests for FixedCapacityPooledMemoryStream

[antonfirsov]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following matches the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
• I have provided test coverage for my change (where applicable)

Description

Forgot to add tests in #1223

[codecov]

Codecov Report

Merging #1225 into master will decrease coverage by 0.00%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master    #1225      +/-   ##
==========================================
- Coverage   82.54%   82.54%   -0.01%     
==========================================
  Files         697      697              
  Lines       30506    30510       +4     
  Branches     3467     3468       +1     
==========================================
+ Hits        25181    25183       +2     
- Misses       4606     4607       +1     
- Partials      719      720       +1     

Flag	Coverage Δ
#unittests	82.54% <50.00%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
...c/ImageSharp/IO/FixedCapacityPooledMemoryStream.cs	86.66% <50.00%> (-13.34%)	⬇️

---

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 bbf3233...be64e51. Read the comment docs.