feat: Add Rand and Trunc expressions

[Linchin]

TODO:

• verify docstring

[gemini-code-assist]

Summary of Changes

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This pull request enhances the Firestore client library by introducing a new Rand expression. This addition provides users with the capability to incorporate pseudorandom number generation directly into their pipeline expressions, which can be useful for various data manipulation and testing scenarios. The change is accompanied by both unit and system tests to ensure its correctness and expected behavior.

Highlights

• New Expression Added: Introduced the Rand expression to the Firestore client library, enabling the generation of pseudorandom floating-point numbers within pipeline expressions.
• System Test Coverage: Added a new system test case in math.yaml to verify that the Rand expression produces values between 0.0 (inclusive) and 1.0 (exclusive).
• Unit Test Coverage: Included a unit test for the Rand expression in test_pipeline_expressions.py to ensure its proper instantiation and attribute values.

Changelog

• packages/google-cloud-firestore/google/cloud/firestore_v1/pipeline_expressions.py
  • Added Rand class, a new FunctionExpression for generating pseudorandom floats.
• packages/google-cloud-firestore/tests/system/pipeline_e2e/math.yaml
  • Appended a system test case to validate the Rand expression's output range.
• packages/google-cloud-firestore/tests/unit/v1/test_pipeline_expressions.py
  • Included a unit test for the Rand expression to confirm its basic functionality.

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[gemini-code-assist]

Code Review

This pull request adds a Rand expression for Firestore pipelines, along with corresponding unit and system tests. The implementation of the Rand expression itself looks good.

However, I found a logical flaw in the system test for Rand, where it uses two separate calls to Rand() to check if the value is within a range, which doesn't guarantee that a single random number is within that range. I've left a suggestion to improve the test.

Also, the pull request title mentions adding a Trunc expression, but it doesn't seem to be included in the changes. This might be intentional, but it's worth clarifying.

_{Note: Security Review did not run due to the size of the PR.}

I am having trouble creating individual review comments. Click here to see my feedback.

packages/google-cloud-firestore/tests/system/pipeline_e2e/math.yaml (316-322)

This test is logically flawed because it calls Rand() twice within the And expression. This means two different random numbers will be generated, and the test is checking if rand1 >= 0.0 and rand2 < 1.0. This doesn't correctly verify that a single random number is within the [0.0, 1.0) range.

For example, if the first Rand() returned 2.0 and the second returned 0.5, the expression (2.0 >= 0.0) AND (0.5 < 1.0) would evaluate to true, even though 2.0 is outside the expected range.

A more robust test would use the result of a single Rand() call. Since the PR title mentions Trunc, I assume a Trunc expression is available or will be soon. You could use it to verify the range with a single Rand() call, which would be a much stronger guarantee of correctness.

            - FunctionExpression.equal:
                - FunctionExpression.trunc:
                    - Rand: []
                - Constant: 0.0

[daniel-sanche]

LGTM