This PR introduces a new analyzer to help users migrate away from Assert API overloads that use format parameters, which will be deprecated in MSTest v4. The analyzer detects usage of the string format, params object[] parameters pattern and provides automated code fixes.

Problem

MSTest v4 will remove Assert API overloads that accept format strings with parameter arrays, such as:

Assert.IsTrue(condition, "Value: {0}", value);
Assert.AreEqual(expected, actual, "Expected {0} but got {1}", expected, actual);
CollectionAssert.AreEqual(list1, list2, "Collections differ: {0}", details);

Users need guidance and tooling to migrate to supported alternatives before upgrading.

Solution

The new MSTEST0053 analyzer detects calls to Assert, CollectionAssert, and StringAssert methods that use the deprecated format parameter pattern by identifying method signatures with:

• Second-to-last parameter: string with [StringSyntax("CompositeFormat")] attribute
• Last parameter: params object[]

Code Fixes

Two automated code fix options are provided:

1. String.Format (Always Available)

// Before
Assert.IsTrue(condition, "Value: {0}", value);

// After  
Assert.IsTrue(condition, string.Format("Value: {0}", value));

2. Interpolated String (For String Literals)

// Before
Assert.IsTrue(condition, "Value: {0}", value);

// After
Assert.IsTrue(condition, $"Value: {value}");

The interpolated string fix is only offered for string literals to ensure safety, while the string.Format fix is always available for any format string expression.

Implementation Details

• Analyzer: AvoidAssertFormatParametersAnalyzer detects the deprecated pattern across all Assert family classes
• Code Fix: AvoidAssertFormatParametersFixer provides both migration options with proper parameter mapping
• Diagnostic ID: MSTEST0053 with Warning severity
• Test Coverage: Comprehensive unit tests covering all Assert types and edge cases

This analyzer helps users proactively prepare their codebases for MSTest v4 while providing flexible migration options based on their preferences and code complexity.

Fixes #6293.

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