Enhance googlecloudmonitoringreceiver: Add Unit Tests for Metric Conversion and Improve Edge Case Coverage

[scaletech-milan]

Description:
Added comprehensive test cases for the entire Google Cloud Monitoring Receiver component.

Link to tracking Issue:
#36815

Testing:
Implemented test cases to validate:

• GCP Monitoring client connection.
• OpenTelemetry's built-in functions.
• Scraping logic.
• Metric conversion functions.

Documentation:
N/A

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: scaletech-milan (2ec6d25, 83e2678, 62ed760, 6be0f2d, ded4121, e34b333, 1e4a060)

[dashpole]

looks good overall. Lets just make the tests less fragile.

[scaletech-milan]

Updated all the changes

[dashpole]

Looks good. Just needs the CLA signed, and I think we are good to go

[scaletech-milan]

Looks good. Just needs the CLA signed, and I think we are good to go

i already proceed for CLA sign, waiting for approval.

[dashpole]

Ah, looks like there are linter failures: https://github.com/open-telemetry/opentelemetry-collector-contrib/actions/runs/12367918994/job/34537235029?pr=36846

[scaletech-milan]

Can you please check now @dashpole

[dashpole]

Run make checkapi
  make checkapi
  shell: /usr/bin/bash -e {0}
  env:
    TEST_RESULTS: testbed/tests/results/junit/results.xml
    SEGMENT_DOWNLOAD_TIMEOUT_MINS: [2](https://github.com/open-telemetry/opentelemetry-collector-contrib/actions/runs/12414428726/job/34674820908?pr=36846#step:10:2)
go run cmd/checkapi/main.go .
Ignoring extension/observer per allowlist
Ignoring extension/opampcustommessages per allowlist
202[4](https://github.com/open-telemetry/opentelemetry-collector-contrib/actions/runs/12414428726/job/34674820908?pr=36846#step:10:4)/12/19 19:28:44 receiver/googlecloudmonitoringreceiver has more than one function: "NewFactory,NewFakeMetricTestServer"

Consider making NewFakeMetricTestServer and other testing-related artifacts not exported (lowercase)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.86%. Comparing base (defc07b) to head (ded4121).
Report is 43 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #36846      +/-   ##
==========================================
+ Coverage   79.72%   79.86%   +0.13%     
==========================================
  Files        2218     2218              
  Lines      209156   209252      +96     
==========================================
+ Hits       166749   167118     +369     
+ Misses      36836    36557     -279     
- Partials     5571     5577       +6     

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[scaletech-milan]

@TylerHelmuth @dashpole
Can you please give workflow approval ?