[Routing] Added Router tests and fixed an exception message.
merged branch jakzal/2.3-router-tests (PR #8102)

This PR was merged into the 2.3 branch.

Discussion
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[Routing] Added Router tests and fixed an exception message

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Commits
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e61ba7d [Routing] Added Router tests and fixed an exception message.