Adds Montrealer tests

[yaniccd]

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[nquesada]

Also, you need pass black

[codecov[bot]]

Codecov Report

Merging #375 (a7f1d5f) into montrealer (1b71163) will increase coverage by 1.83%. The diff coverage is 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## montrealer #375 +/- ## =============================================== + Coverage 98.16% 100.00% +1.83% =============================================== Files 28 28 Lines 1961 1972 +11 =============================================== + Hits 1925 1972 +47 + Misses 36 0 -36 ``` | [Files](https://app.codecov.io/gh/XanaduAI/thewalrus/pull/375?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI) | Coverage Δ | | |---|---|---| | [thewalrus/\_montrealer.py](https://app.codecov.io/gh/XanaduAI/thewalrus/pull/375?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI#diff-dGhld2FscnVzL19tb250cmVhbGVyLnB5) | `100.00% <ø> (+40.00%)` | :arrow_up: | | [thewalrus/reference.py](https://app.codecov.io/gh/XanaduAI/thewalrus/pull/375?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI#diff-dGhld2FscnVzL3JlZmVyZW5jZS5weQ==) | `100.00% <100.00%> (+24.56%)` | :arrow_up: | ------ [Continue to review full report in Codecov by Sentry](https://app.codecov.io/gh/XanaduAI/thewalrus/pull/375?src=pr&el=continue&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI). > **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI) > `Δ = absolute (impact)`, `ø = not affected`, `? = missing data` > Powered by [Codecov](https://app.codecov.io/gh/XanaduAI/thewalrus/pull/375?src=pr&el=footer&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI). Last update [1b71163...a7f1d5f](https://app.codecov.io/gh/XanaduAI/thewalrus/pull/375?src=pr&el=lastupdated&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=XanaduAI).