Test: Standardize Exception Testing Patterns

[nickna]

Description

Standardize exception testing across all test files to use consistent NUnit patterns and improve test reliability.

Phase

Phase 0: Test Technical Debt Cleanup

Epic

Related to #202

Acceptance Criteria

• Audit all exception testing patterns in test files
• Standardize on Assert.Throws<T>() pattern
• Ensure exception messages are validated where appropriate
• Remove inconsistent exception testing approaches
• Add missing exception tests for edge cases

Current Inconsistencies

• Mix of Assert.Throws, try-catch blocks, and ExpectedException attributes
• Inconsistent validation of exception messages
• Some tests only check exception type, not message content

Preferred Pattern

// PREFERRED: Modern NUnit pattern
var ex = Assert.Throws<ArgumentNullException>(() => database.AddVector(null));
Assert.That(ex.ParamName, Is.EqualTo("vector"));

// PREFERRED: For async methods
var ex = Assert.ThrowsAsync<ArgumentOutOfRangeException>(async () => 
    await database.SearchAsync(query, -1));
Assert.That(ex.Message, Contains.Substring("k must be positive"));

Files to Review

• All test files with exception testing
• Focus on argument validation tests
• Search algorithm parameter validation
• Database operation error conditions