- поправил строку подключения.

- .net 6.0 => .net 5.0

PhoneStore.Tests/Helpers/Utilities.cs

@@ -10,7 +10,7 @@ namespace PhoneStore.Tests.Helpers
     public static class Utilities
     {
         private const string ConnectionString =
-            "Server=localhost;Port=54320;database=testDb;Username=postgres;Password=postgres;";
+            "Server=localhost;Port=5432;database=testDb;Username=postgres;Password=postgres;";
         public static WebApplicationFactory<Startup> SubstituteDbOnTestDb()
         {
             return new WebApplicationFactory<Startup>().WithWebHostBuilder(builder =>

PhoneStore.Tests/PhoneStore.Tests.csproj

 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFramework>net5.0</TargetFramework>
+        <TargetFramework>net6.0</TargetFramework>
 
         <IsPackable>false</IsPackable>
     </PropertyGroup>

PhoneStore/PhoneStore.csproj

 <Project Sdk="Microsoft.NET.Sdk.Web">
 
     <PropertyGroup>
-        <TargetFramework>net5.0</TargetFramework>
+        <TargetFramework>net6.0</TargetFramework>
     </PropertyGroup>
 
     <ItemGroup>

PhoneStore/appsettings.json

 {
   "ConnectionStrings": {
-    "DefaultConnection": "Server=localhost;Port=54320;database=lesson68;Username=postgres;Password=postgres;"
+    "DefaultConnection": "Server=localhost;Port=5432;database=testDb;Username=postgres;Password=postgres;"
   },
   "Logging": {
     "LogLevel": {