Add a multi-package mode to `dpm test`, similar to `dpm build --all`

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What is the problem you want to solve?

In a multi-package project, no single command runs the tests of all the packages in multi-package.yaml.

dpm build --all builds all the packages in multi-package.yaml. But dpm test --all has a different meaning: it runs the tests of the current package and its dependencies only. Thus, to run all the testSettle scripts in the project, I must go to each package and run dpm test --test-pattern testSettle.

IMPORTANT: the fact that dpm test --all includes dependency tests in a test run is very counterintuitive. This flag should have been reserved for the multi-package mode, similar to dpm build --all. A different flag like dpm test --include-dependencies would be more appropriate, but this would be a breaking change.

What is the solution you would propose?

Add a way to run the tests of all the packages in multi-package.yaml from the root of the project, for example:

dpm test --all-packages --test-pattern testSettle

The flag name is only an example. As noted previously, if you change the meaning of --all to match dpm build --all, this breaks the current behavior, so a new flag is possibly better.

The command should:

• Build each package one time.
• Run the tests of each package one time, also if other packages depend on it.
• Print one summary for the project.

Describe alternatives you've considered

1. A shell loop over the packages:

dpm build --all
in_packages=false
while IFS= read -r -u 3 line; do
  if [[ $line =~ ^packages:[[:space:]]*$ ]]; then
    in_packages=true
  elif $in_packages && [[ $line =~ ^[[:space:]]*-[[:space:]]+([^#[:space:]]+) ]]; then
    pkg=${BASH_REMATCH[1]//[\"\']/}
    (cd "$pkg" && dpm test --test-pattern testSettle) || exit 1
  elif [[ $line =~ ^[^[:space:]#-] ]]; then
    in_packages=false
  fi
done 3< multi-package.yaml

This parses multi-package.yaml with a simple line match, prints one summary for each package, and does not give one coverage report.

2. Run dpm test --all in a test package that depends on all the other packages. This misses the packages that are not dependencies of that package.

Additional context

SDK version: 3.5.8 dpm version: 1.0.22

Rust's cargo has this behavior: cargo test --workspace test_settle runs the matching tests in all the workspace members, and cargo test -p <package> selects one package from the root.