svrnty-mcp-gateway/tests/Svrnty.MCP.Gateway.Core.Tests/Interfaces/ICircuitBreakerTests.cs

using Xunit;
using Moq;
using Svrnty.MCP.Gateway.Core.Interfaces;

namespace Svrnty.MCP.Gateway.Core.Tests.Interfaces;

/// <summary>
/// Unit tests for ICircuitBreaker interface following TDD approach.
/// Tests circuit breaker pattern implementation.
/// </summary>
public class ICircuitBreakerTests
{
    [Fact]
    public async Task ExecuteAsync_WithClosedCircuit_ExecutesOperation()
    {
        // Arrange
        var mockCircuitBreaker = new Mock<ICircuitBreaker>();
        var expectedResult = "success";

        mockCircuitBreaker
            .Setup(cb => cb.ExecuteAsync(
                It.IsAny<Func<Task<string>>>(),
                It.IsAny<CancellationToken>()))
            .Returns<Func<Task<string>>, CancellationToken>((operation, ct) => operation());

        // Act
        var result = await mockCircuitBreaker.Object.ExecuteAsync(
            async () => await Task.FromResult(expectedResult),
            CancellationToken.None);

        // Assert
        Assert.Equal(expectedResult, result);
    }

    [Fact]
    public async Task ExecuteAsync_WithOpenCircuit_ThrowsException()
    {
        // Arrange
        var mockCircuitBreaker = new Mock<ICircuitBreaker>();

        mockCircuitBreaker
            .Setup(cb => cb.ExecuteAsync(
                It.IsAny<Func<Task<string>>>(),
                It.IsAny<CancellationToken>()))
            .ThrowsAsync(new InvalidOperationException("Circuit is open"));

        // Act & Assert
        await Assert.ThrowsAsync<InvalidOperationException>(() =>
            mockCircuitBreaker.Object.ExecuteAsync(
                async () => await Task.FromResult("result"),
                CancellationToken.None));
    }

    [Fact]
    public void GetState_ReturnsCircuitState()
    {
        // Arrange
        var mockCircuitBreaker = new Mock<ICircuitBreaker>();
        mockCircuitBreaker.Setup(cb => cb.GetState()).Returns("Closed");

        // Act
        var state = mockCircuitBreaker.Object.GetState();

        // Assert
        Assert.Equal("Closed", state);
        mockCircuitBreaker.Verify(cb => cb.GetState(), Times.Once);
    }

    [Fact]
    public void Reset_ResetsCircuitBreaker()
    {
        // Arrange
        var mockCircuitBreaker = new Mock<ICircuitBreaker>();
        mockCircuitBreaker.Setup(cb => cb.Reset()).Verifiable();

        // Act
        mockCircuitBreaker.Object.Reset();

        // Assert
        mockCircuitBreaker.Verify(cb => cb.Reset(), Times.Once);
    }

    [Fact]
    public async Task ExecuteAsync_WithMultipleFailures_OpensCircuit()
    {
        // Arrange
        var mockCircuitBreaker = new Mock<ICircuitBreaker>();
        var callCount = 0;

        mockCircuitBreaker
            .Setup(cb => cb.ExecuteAsync(
                It.IsAny<Func<Task<string>>>(),
                It.IsAny<CancellationToken>()))
            .Returns<Func<Task<string>>, CancellationToken>((operation, ct) =>
            {
                callCount++;
                if (callCount >= 3)
                {
                    throw new InvalidOperationException("Circuit is open");
                }
                return operation();
            });

        // Act & Assert
        // First two calls should succeed
        await mockCircuitBreaker.Object.ExecuteAsync(
            async () => await Task.FromResult("result1"),
            CancellationToken.None);
        await mockCircuitBreaker.Object.ExecuteAsync(
            async () => await Task.FromResult("result2"),
            CancellationToken.None);

        // Third call should fail with open circuit
        await Assert.ThrowsAsync<InvalidOperationException>(() =>
            mockCircuitBreaker.Object.ExecuteAsync(
                async () => await Task.FromResult("result3"),
                CancellationToken.None));
    }
}