Частично покрыл тестами PhoneController.

PhoneStore.Tests/Helpers/Utilities.cs

+using System.Linq;
+using Microsoft.AspNetCore.Mvc.Testing;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using PhoneStore.Models;
+using PhoneStore.ViewModels.PhoneViewModels;
+
+namespace PhoneStore.Tests.Helpers
+{
+    public static class Utilities
+    {
+        private const string ConnectionString =
+            "Server=localhost;Port=54320;database=testDb;Username=postgres;Password=postgres;";
+        public static WebApplicationFactory<Startup> SubstituteDbOnTestDb()
+        {
+            return new WebApplicationFactory<Startup>().WithWebHostBuilder(builder =>
+            {
+                builder.ConfigureServices(services =>
+                {
+                    var dbContextDescriptor =
+                        services.SingleOrDefault(s => s.ServiceType == typeof(DbContextOptions<MobileContext>));
+                    services.Remove(dbContextDescriptor);
+                    services.AddDbContext<MobileContext>(options =>
+                    {
+                        options.UseNpgsql(ConnectionString);
+                    });
+                });
+            });
+        }
+
+        public static int CreateBrandAndReturnBrandId(MobileContext context)
+        {
+            Brand brand = new Brand {Name = "Asus"};
+            context.Brands.Add(brand);
+            context.SaveChanges();
+            return brand.Id;
+        }
+        
+        public static int CreatePhoneAndReturnPhoneId(MobileContext context)
+        {
+            Phone phone = new Phone
+            {
+                Name = "Test",
+                Price = 3000M,
+                Brand = new Brand{Name = "Adidas"}
+            };
+            context.Phones.Add(phone);
+            context.SaveChanges();
+            return phone.Id;
+        }
+    }
+}
\ No newline at end of file

PhoneStore.sln

@@ -2,6 +2,8 @@
 Microsoft Visual Studio Solution File, Format Version 12.00
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "PhoneStore", "PhoneStore\PhoneStore.csproj", "{32DC0801-63D0-4261-9F07-8DD570B35335}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "PhoneStore.Tests", "PhoneStore.Tests\PhoneStore.Tests.csproj", "{3DF8B5C0-BB98-4A2E-A589-5311ECBE546D}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -12,5 +14,9 @@ Global
 		{32DC0801-63D0-4261-9F07-8DD570B35335}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{32DC0801-63D0-4261-9F07-8DD570B35335}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{32DC0801-63D0-4261-9F07-8DD570B35335}.Release|Any CPU.Build.0 = Release|Any CPU
+		{3DF8B5C0-BB98-4A2E-A589-5311ECBE546D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{3DF8B5C0-BB98-4A2E-A589-5311ECBE546D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{3DF8B5C0-BB98-4A2E-A589-5311ECBE546D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{3DF8B5C0-BB98-4A2E-A589-5311ECBE546D}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 EndGlobal

PhoneStore/Controllers/PhonesController.cs

@@ -54,29 +54,53 @@ namespace PhoneStore.Controllers
             return View(model);
         }
         
+        // [HttpPost]
+        // public async Task<IActionResult> Create(PhoneCreateViewModel model)
+        // {
+        //     try
+        //     {
+        //         if (ModelState.IsValid)
+        //         {
+        //             await _phoneService.CreateAsync(model);
+        //
+        //             return RedirectToAction("Index");
+        //         }
+        //
+        //         model.Brands = _db.Brands.ToList();
+        //         return View("Create", model);
+        //     }
+        //     //TODO: Добавить кастомный exception
+        //     catch (FileNotFoundException)
+        //     {
+        //         return RedirectToAction("Error", "Errors", new {statusCode = 666});
+        //     }
+        //     catch(Exception)
+        //     {
+        //         return RedirectToAction("Error", "Errors", new {statusCode = 777});
+        //     }
+        // }
+        
         [HttpPost]
-        public async Task<IActionResult> Create(PhoneCreateViewModel model)
+        public async Task<IActionResult> Create([FromBody]PhoneCreateViewModel model)
         {
             try
             {
                 if (ModelState.IsValid)
                 {
                     await _phoneService.CreateAsync(model);
-
-                    return RedirectToAction("Index");
+                    return Ok();
                 }
 
                 model.Brands = _db.Brands.ToList();
-                return View("Create", model);
+                return ValidationProblem();
             }
-            //TODO: Добавить кастомный exception
             catch (FileNotFoundException)
             {
-                return RedirectToAction("Error", "Errors", new {statusCode = 666});
+                return BadRequest();
             }
             catch(Exception)
             {
-                return RedirectToAction("Error", "Errors", new {statusCode = 777});
+                return BadRequest();
             }
         }
 
@@ -138,19 +162,34 @@ namespace PhoneStore.Controllers
             return RedirectToAction("Index");
         }
 
+        // [HttpGet]
+        // public IActionResult About(int? phoneId)
+        // {
+        //     try
+        //     {
+        //         if (!phoneId.HasValue) return RedirectToAction("Error", "Errors", new {statusCode = 777});
+        //         var phoneViewModel = _phoneService.GetById(phoneId.Value);
+        //         return View(phoneViewModel);
+        //     }
+        //     catch (NullReferenceException)
+        //     {
+        //         return RedirectToAction("Error", "Errors", new {statusCode = 777});
+        //     }
+        // }
         [HttpGet]
         public IActionResult About(int? phoneId)
         {
             try
             {
-                if (!phoneId.HasValue) return RedirectToAction("Error", "Errors", new {statusCode = 777});
+                if (!phoneId.HasValue) return ValidationProblem();
                 var phoneViewModel = _phoneService.GetById(phoneId.Value);
-                return View(phoneViewModel);
+                return Ok(phoneViewModel);
             }
             catch (NullReferenceException)
             {
-                return RedirectToAction("Error", "Errors", new {statusCode = 777});
+                return BadRequest();
             }
         }
+        
     }
 }
\ No newline at end of file

PhoneStore/Models/Brand.cs

+using System.Text.Json.Serialization;
+
 namespace PhoneStore.Models
 {
     public class Brand
     {
+        [JsonPropertyName("id")]
         public int Id { get; set; }
+        [JsonPropertyName("name")]
         public string Name { get; set; }
     }
 }
\ No newline at end of file

PhoneStore/Startup.cs

@@ -39,11 +39,11 @@ namespace PhoneStore
             if (env.IsDevelopment())
             {
                 app.UseDeveloperExceptionPage();
-                app.UseStatusCodePagesWithRedirects("/Error/{0}");
+                // app.UseStatusCodePagesWithRedirects("/Error/{0}");
             }
             else
             {
-                app.UseExceptionHandler("/Home/Error");
+                // app.UseExceptionHandler("/Home/Error");
                 app.UseHsts();
             }
 

PhoneStore/ViewModels/BaseEntity.cs

+using System.Text.Json.Serialization;
+
 namespace PhoneStore.ViewModels
 {
     public class BaseEntity
     {
+        [JsonPropertyName("id")]
         public int Id { get; set; }
     }
 }
\ No newline at end of file

PhoneStore/ViewModels/PhoneViewModels/PhoneViewModel.cs

 using System.Collections.Generic;
+using System.Text.Json.Serialization;
 using PhoneStore.Models;
 using PhoneStore.ViewModels.Feedback;
 
@@ -6,11 +7,17 @@ namespace PhoneStore.ViewModels.PhoneViewModels
 {
     public class PhoneViewModel : BaseEntity
     {
+        [JsonPropertyName("name")]
         public string Name { get; set; }
+        [JsonPropertyName("price")]
         public decimal Price { get; set; }
+        [JsonPropertyName("brandId")]
         public int BrandId { get; set; }
+        [JsonPropertyName("brand")]
         public Brand Brand { get; set; }
+        [JsonPropertyName("image")]
         public string Image { get; set; }
+        [JsonPropertyName("feedbacks")]
         public IEnumerable<FeedbackViewModel> Feedbacks { get; set; }
     }
 }
\ No newline at end of file