Split TestCursor into separate test functions.

[matthewdale]

Summary

• Move subtests in TestCursor that test specific Cursor methods into separate test functions.

Background & Motivation

Very long test functions with deeply-nested subtests are difficult to read, maintain, and run. It's better to split up some subtests into separate test functions.

[mongodb-drivers-pr-bot]

API Change Report

No changes found!

[mongodb-drivers-pr-bot]

🧪 Performance Results

Commit SHA: bd7c125

The following benchmark tests for version 68b223d9f4c093000717cac8 had statistically significant changes (i.e., |z-score| > 1.96):

Benchmark	Measurement	% Change	Patch Value	Stable Region	H-Score	Z-Score
BenchmarkMultiFindMany	total_time_seconds	19.1047	1.3171	Avg: 1.1059 Med: 1.0549 Stdev: 0.1050	0.7361	2.0113
BenchmarkSmallDocInsertOne	total_time_seconds	-3.8070	1.1389	Avg: 1.1840 Med: 1.1849 Stdev: 0.0218	0.7359	-2.0657
BenchmarkBSONDeepDocumentDecoding	total_bytes_allocated	-3.2530	243667288.0000	Avg: 251860213.4194 Med: 252330328.0000 Stdev: 3023314.2474	0.7931	-2.7099
BenchmarkBSONDeepDocumentDecoding	total_mem_allocs	-3.1986	11219121.0000	Avg: 11589832.4194 Med: 11611115.0000 Stdev: 138499.4358	0.7903	-2.6766
BenchmarkBSONDeepDocumentDecoding	total_time_seconds	-1.5791	1.1803	Avg: 1.1993 Med: 1.1989 Stdev: 0.0058	0.8506	-3.2554
BenchmarkBSONFullDocumentEncoding	total_time_seconds	1.5400	1.2128	Avg: 1.1944 Med: 1.1937 Stdev: 0.0082	0.7541	2.2468
BenchmarkBSONDeepDocumentDecoding	allocated_bytes_per_op	-0.0543	15095.0000	Avg: 15103.1935 Med: 15104.0000 Stdev: 2.3723	0.9090	-3.4538

For a comprehensive view of all microbenchmark results for this PR's commit, please check out the Evergreen perf task for this patch.

[Copilot]

Pull Request Overview

This pull request refactors the TestCursor function by splitting its nested subtests into separate, independent test functions. This improves test maintainability and readability by reducing the complexity of deeply-nested test structures.

Key changes:

• Extracted four subtests from TestCursor into standalone test functions: TestCursor_TryNext, TestCursor_RemainingBatchLength, TestCursor_All, and TestCursor_Close
• Moved the "set batchSize" subtest to remain within the original TestCursor function
• Relocated variable declarations to their appropriate scopes in the new test functions

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[prestonvasquez]

It's not part of the changes in this PR but assertCursorBatchLength should call mt.Helper().

[matthewdale]

I removed assertCursorBatchLength because it can be condensed into a single assert call, making the test easier to read.