Add allocation window equivalence test

[Noah-Philip]

Description

Adds an allocation window parsing consistency test.

The test queries /allocation using supported keyword windows:

• today
• yesterday
• week

For each keyword window, it builds an equivalent explicit RFC3339 range from the response window and verifies that the explicit range returns a consistent allocation total.

Implementation

• Uses the same allocation query parameters for each keyword and explicit range
• Uses aggregate=namespace, accumulate=true, and includeIdle=true
• Builds explicit RFC3339 ranges from the API-returned keyword window
• Compares summed totalCost between keyword and explicit range responses
• Uses absolute and relative tolerances for small rounding differences

Testing

• go test -count=1 ./test/integration/api/allocation -run TestAllocationKeywordAndExplicitWindowsEquivalent -v
• bats test/integration/api/allocation/test.bats

[Copilot]

Pull request overview

This PR adds a new OpenCost integration test that validates allocation window-parsing consistency. For each supported keyword window (today, yesterday, week, 14d), it queries /allocation, rebuilds an equivalent explicit RFC3339 range from the API-returned window, re-queries, and asserts the summed totalCost matches within absolute/relative tolerances. It fits alongside the existing window-related tests (e.g., correct_window_values_test.go) in the allocation integration suite.

Changes:

• Adds allocation_window_equivalence_test.go implementing TestAllocationKeywordAndExplicitWindowsEquivalent with self-contained helpers for fetching, summing, window extraction, RFC3339 formatting, and tolerance comparison.
• Registers the new test in test.bats so it runs as part of the allocation suite.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
test/integration/api/allocation/allocation_window_equivalence_test.go	New integration test comparing keyword vs. explicit RFC3339 window allocation totals with tolerance handling.
test/integration/api/allocation/test.bats	Adds a bats entry to execute the new equivalence test.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Manas23601]

I appreciate the thought that went into writing this test, but I feel this would be a better fit as a unit test.
https://github.com/opencost/opencost/blob/develop/core/pkg/opencost/window.go#L146 - Perhaps a unit test for this function would serve your objective?

@ameijer, What do you think?