feat(testing): Add Parameterized Test Support with Test Data Generator

[Mustafa11300]

🔍 Description

Adds parameterized scenario expansion to the mofa-testing crate. A single scenario template can now expand into many concrete test cases by substituting {{variable}} placeholders with values from parameter sets.

This is Issue 3 from the testing platform roadmap (Test Definition Layer, Phase 2).

Closes #1603
Depends on #1599

📌 Changes

New: tests/src/parameterized.rs

Core parameterized test module with the following public components:

Component	Purpose
ParameterSet	Named map of variable → value bindings for one test variant
ParameterMatrix	Cartesian product expansion with configurable safety limits
ParameterizedScenario	Wraps an AgentTestScenario template and expands it against parameter sets
ParameterizedScenarioFile	YAML/TOML/JSON file-backed parameterized scenario loading
ParameterExpansionError	Structured error type for all expansion failure modes

Placeholder substitution ({{variable}}) is supported in:

• user_input (turn prompts)
• system_prompt
• text expectations (respond_containing, respond_exact)
• pattern expectations (respond_matching_regex)
• name expectations (call_tool, call_tool_with)
• arguments values (recursively in JSON)

Expansion modes:

• Explicit parameter list: named sets with direct variable bindings
• Matrix expansion: Cartesian product of variable dimensions
• Mixed: both explicit and matrix sets combined

Modified: tests/src/lib.rs

• Added pub mod parameterized module registration
• Added public re-exports: ParameterExpansionError, ParameterMatrix, ParameterSet, ParameterizedScenario, ParameterizedScenarioFile

New: tests/tests/parameterized_tests.rs

30+ comprehensive tests covering:

• ParameterSet: builder, variable ordering, serialization roundtrip
• ParameterMatrix: 1/2/3 dimensions, combination count, empty dimension error, no dimensions error, limit exceeded error
• Expansion: placeholder substitution in all field types (user_input, system_prompt, respond_containing, respond_exact, respond_matching_regex, call_tool_with arguments)
• Execution: expanded scenarios run with agents and produce correct reports; failure detection in parameterized variants
• File loading: YAML, TOML, JSON parameterized scenario files; matrix expansion from files; mixed explicit + matrix; file-level limit enforcement
• Edge cases: no placeholders, multiple placeholders in single field, same placeholder used multiple times, missing variable detection, empty parameter sets, stable naming

New: examples/parameterized_test/

File	Description
README.md	Usage guide with code samples and placeholder syntax reference
scenario_weather_parameterized.yaml	Explicit parameter list: weather lookup across 3 cities
scenario_greetings_matrix.yaml	Matrix expansion: 2 languages × 3 tones = 6 variants
scenario_support_parameterized.toml	TOML: parameterized support ticket lookup across departments

🧪 Testing

All new functionality is covered by tests/tests/parameterized_tests.rs with 30+ test cases.

Key test categories:

1. Unit tests — ParameterSet and ParameterMatrix in isolation
2. Integration tests — Full expansion + scenario execution with ScriptedAgent
3. File loading tests — YAML, TOML, JSON deserialization and expansion
4. Error path tests — Empty sets, missing variables, matrix limit exceeded, empty dimensions
5. Edge case tests — No placeholders, multiple placeholders, stable naming, serialization

💡 Usage Example

Builder API (Rust)

use mofa_testing::{AgentTest, ParameterSet, ParameterMatrix, ParameterizedScenario};

// 1. Define a template with {{variable}} placeholders
let template = AgentTest::new("weather_agent")
    .given_tool("weather_search")
    .when_user_says("What's the weather in {{city}}?")
    .then_agent_should()
    .call_tool("weather_search")
    .respond_containing("{{city}}")
    .build()?;

// 2. Define parameter sets (explicit or matrix)
let sets = ParameterMatrix::new()
    .dimension("city", vec!["Berlin", "Tokyo", "NYC"])
    .expand()?;

// 3. Expand and run
let parameterized = ParameterizedScenario::new(template, sets);
let expanded = parameterized.expand()?; // 3 concrete scenarios

for scenario in &expanded {
    let report = scenario.run_with_agent(&mut agent).await;
    println!("[{}] passed={}", scenario.agent_id, report.passed());
}

File-backed (YAML)

template:
  agent_id: weather_agent
  tools: [weather_search]
  turns:
    - user: "What's the weather in {{city}}?"
      expect:
        - kind: call_tool
          name: weather_search
        - kind: respond_containing
          text: "{{city}}"

parameters:
  - name: berlin
    vars: { city: Berlin }
  - name: tokyo
    vars: { city: Tokyo }

let yaml = std::fs::read_to_string("scenario.yaml")?;
let parameterized = ParameterizedScenarioFile::from_yaml_str(&yaml)?;
let expanded = parameterized.expand()?;

✅ Checklist

• Code follows project conventions and style
• New module registered in lib.rs with public re-exports
• Comprehensive tests added (parameterized_tests.rs)
• Examples added (examples/parameterized_test/)
• README with usage documentation included
• Error handling with structured error types
• No breaking changes to existing APIs
• Builds on the DSL foundation from feat(testing): Add Agent Test DSL with Declarative Scenario Builder #1599