title: How to share one fixture among all test classes?
body: <p>I want to share DBfixture in all tests. This is the collection created for this purpose:</p>
  <pre><code>[CollectionDefinition(&quot;db&quot;)]
  public class TestColDefinition : IClassFixture&lt;DBfixture&gt; {  }
  </code></pre>
  <p>I have a base class from which i derive my test classes:</p>
  <pre><code>public class TestBase
  {
      protected readonly ITestOutputHelper testOutputHelper;
      protected DBfixture dbf;
  
      public TestBase(ITestOutputHelper testOutputHelper, DBfixture dbf)
      {
          this.testOutputHelper = testOutputHelper;
          this.dbf = dbf;
      }
  }
  
  [Collection(&quot;db&quot;)]
  public class TestClass1 :  TestBase
  {
      public TestClass1(ITestOutputHelper testOutputHelper, DBfixture dbf) : base(testOutputHelper, dbf) { }
  
      [Fact]
      public void fact(){}
  }
  
  [Collection(&quot;db&quot;)]
  public class TestClass2 :  TestBase
  {
      public TestClass2(ITestOutputHelper testOutputHelper, DBfixture dbf) : base(testOutputHelper, dbf) { }
  
      [Fact]
      public void fact(){}
  }
  </code></pre>
  <p>But when I run tests two DBfixture objects are created (one for each test class). Without collection four objects are created. How do I setup this so that one object is shared among all test classes?</p>