Fix some inconsistencies in tests (#1501)

Author: bkoelman

Diff for: test/JsonApiDotNetCoreTests/IntegrationTests/ReadWrite/Deleting/DeleteResourceTests.cs

@@ -45,9 +45,9 @@ await _testContext.RunOnDatabaseAsync(async dbContext =>
 
         await _testContext.RunOnDatabaseAsync(async dbContext =>
         {
-            WorkItem? workItemsInDatabase = await dbContext.WorkItems.FirstWithIdOrDefaultAsync(existingWorkItem.Id);
+            WorkItem? workItemInDatabase = await dbContext.WorkItems.FirstWithIdOrDefaultAsync(existingWorkItem.Id);
 
-            workItemsInDatabase.Should().BeNull();
+            workItemInDatabase.Should().BeNull();
         });
     }
 

Diff for: test/JsonApiDotNetCoreTests/IntegrationTests/ReadWrite/Fetching/FetchResourceTests.cs

@@ -230,7 +230,7 @@ await _testContext.RunOnDatabaseAsync(async dbContext =>
     }
 
     [Fact]
-    public async Task Can_get_unknown_secondary_OneToMany_resource()
+    public async Task Can_get_unknown_secondary_OneToMany_resources()
     {
         // Arrange
         UserAccount userAccount = _fakers.UserAccount.Generate();