Add comprehensive test coverage for course creation feature

[Copilot]

The course creation feature lacked test coverage despite having full implementation in place (entities, DTOs, services, validators, and API endpoints).

Changes

Test Infrastructure

• Added CourseRegistration.Application.Tests with xUnit, Moq, FluentAssertions
• Added CourseRegistration.API.Tests with Microsoft.AspNetCore.Mvc.Testing
• Made Program class accessible via partial declaration for integration testing

Unit Tests (11 tests)

CourseService.CreateCourseAsync (6 tests)

• Valid creation flow with mapper and repository mocks
• Date validation: start date future constraint, end date ordering
• Edge cases: equal dates, optional fields, GUID generation

CreateCourseDtoValidator (5 tests)

• FluentValidation rules: required fields, length constraints, date logic
• Course duration constraints (7-365 days)

Integration Tests (4 tests)

POST /api/courses

• Happy path returns 201 with location header
• Invalid dates return 400 via service-layer validation
• Response format validation with JSON deserialization

Example

[Fact]
public async Task CreateCourseAsync_WithStartDateInPast_ShouldThrowInvalidOperationException()
{
    var createCourseDto = new CreateCourseDto
    {
        StartDate = DateTime.UtcNow.AddDays(-5), // Past date
        EndDate = DateTime.UtcNow.AddDays(30),
        // ... other fields
    };

    var exception = await Assert.ThrowsAsync<InvalidOperationException>(
        () => _courseService.CreateCourseAsync(createCourseDto));
    
    exception.Message.Should().Contain("must be in the future");
    _mockCourseRepository.Verify(r => r.AddAsync(It.IsAny<Course>()), Times.Never);
}

All 15 tests passing. CodeQL scan clean.

Original prompt

create a new issue for add course feature

The user has attached the following file paths as relevant context:

• .github\instructions\agents.md.instructions.md
• .github\instructions\dotnet-dev.instructions.md

Created from VS Code via the GitHub Pull Request extension.

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