Union code coverage across all six pipelines

[aaronburtle]

Why make this change?

Closes #3715

What is this change?

• Adds a best-effort Total Code Coverage job to the existing unit-test
  pipeline (unittest-pipelines.yml) that surfaces the true combined coverage
  across all six test pipelines, instead of the misleadingly low per-pipeline
  numbers.
  • DAB's tests are split across six independent ADO pipelines (unit + MsSql,
    PostgreSql, MySql, DwSql, CosmosDb). Each publishes its own coverage tab and
    nothing merges them, so every pipeline in isolation reads much lower than the union.
• How it works:
  • The build job publishes this run's unit cobertura as a coverage-unit
    pipeline artifact.
  • The new total_code_coverage job (dependsOn: build) downloads that plus the
    latest available cobertura from the five DB pipelines
    (DownloadPipelineArtifact@2, definition IDs DwSql=1, MsSql=2, MySql=3,
    PgSql=4, Cosmos=6).
  • scripts/merge-coverage.ps1 unions all reports and emits one combined
    Cobertura.xml, which PublishCodeCoverageResults@2 publishes.
• Design notes:
  • Rolling dashboard, not a synchronized per-PR gate. DB coverage is pulled
    with runVersion: latest, so it may reflect an older commit ADO offers no
    primitive to block on all six sibling runs from inside one of them. A true
    per-PR guarantee would require consolidating all suites into one pipeline with
    a dependsOn-all aggregation job. This is not necessary for tracking code coverage.
  • Best-effort: continueOnError on the job and every step, so it can never
    fail or block unit CI. If aggregation fails, the build job's own unit-only
    coverage remains as the tab fallback.
  • The merge keys on fully-qualified class name + line (agent-path independent)
    so points union correctly across Windows/Linux agents, and excludes *.Tests
    assemblies.

How was this tested?

• Integration Tests
• Unit Tests

Validated scripts/merge-coverage.ps1 locally against real cobertura from all six
pipelines (combined = 76.77% branch / 83.33% line) and against synthetic reports
covering cross-agent path union, branch-condition max-merge, test-assembly
exclusion, and well-formed Cobertura output. Pipeline changes are CI-only.

Sample Request(s)

• N/A — CI/pipeline change only; no REST, GraphQL, or CLI surface is affected.
• Local usage of the merge script:

  ./scripts/merge-coverage.ps1 -Path <folder-of-cobertura> -OutFile combined/Cobertura.xml
  

[Copilot]

Pull request overview

This PR adds a “Total Code Coverage” aggregation mechanism to provide a more accurate combined (union) coverage number across DAB’s six independent Azure DevOps pipelines by downloading each pipeline’s Cobertura output and merging them into a single report.

Changes:

• Introduces scripts/merge-coverage.ps1, a dependency-free Cobertura union merger that can also emit a merged Cobertura XML for publishing.
• Updates the unit-test pipeline to publish its coverage as a pipeline artifact and adds a new best-effort job that downloads latest DB-pipeline coverage and publishes a combined coverage report.
• Extends the shared build/unit-test template to stage and publish the unit coverage artifact used by the aggregation job.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
scripts/merge-coverage.ps1	Adds a PowerShell Cobertura union-merger (line + branch) and optional merged XML emitter.
.pipelines/unittest-pipelines.yml	Converts the unit pipeline to multi-job and adds a best-effort “Total Code Coverage” aggregation job.
.pipelines/templates/build-pipelines.yml	Publishes unit Cobertura files as a pipeline artifact (coverage-unit) for later aggregation.