Here's a little bit of that history.

## Alternatives { #alternatives }

I have been creating APIs with complex requirements for several years (Machine Learning, distributed systems, asynchronous jobs, NoSQL databases, etc), leading several teams of developers.

As part of that, I needed to investigate, test and use many alternatives.

The history of **FastAPI** is in great part the history of its predecessors.

                    return union(emptySet(), newHashSet(elements));
                  }
                })
            .named("empty U set")
            .withFeatures(
                CollectionSize.ONE, CollectionSize.SEVERAL, CollectionFeature.ALLOWS_NULL_VALUES)
            .createTestSuite());

    suite.addTest(
        SetTestSuiteBuilder.using(
                new TestStringSetGenerator() {
                  @Override

import static com.google.common.collect.testing.features.CollectionFeature.ALLOWS_NULL_VALUES;
import static com.google.common.collect.testing.features.CollectionSize.SEVERAL;
import static com.google.common.collect.testing.features.CollectionSize.ZERO;
import static com.google.common.collect.testing.google.ReflectionFreeAssertThrows.assertThrows;
import static java.util.Arrays.asList;

      assertOneToOne();
    } catch (UnsupportedOperationException tolerated) {
    }
  }

  @CollectionSize.Require(SEVERAL)
  @CollectionFeature.Require(SUPPORTS_ADD)
  public void testSetCount_threeToThree_addSupported() {
    assertThreeToThree();
  }

  @CollectionSize.Require(SEVERAL)
  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testSetCount_threeToThree_removeSupported() {
    assertThreeToThree();

## OAuth2 { #oauth2 }

OAuth2 is a specification that defines several ways to handle authentication and authorization.

It is quite an extensive specification and covers several complex use cases.

It includes ways to authenticate using a "third party".

      assertOneToOne();
    } catch (UnsupportedOperationException tolerated) {
    }
  }

  @CollectionSize.Require(SEVERAL)
  @CollectionFeature.Require(SUPPORTS_ADD)
  public void testSetCount_threeToThree_addSupported() {
    assertThreeToThree();
  }

  @CollectionSize.Require(SEVERAL)
  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testSetCount_threeToThree_removeSupported() {
    assertThreeToThree();

///

### Flask REST frameworks { #flask-rest-frameworks }

There are several Flask REST frameworks, but after investing the time and work into investigating them, I found that many are discontinued or abandoned, with several standing issues that made them unfit.

  }

  @CollectionSize.Require(SEVERAL)
  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testRemoveAllIgnoresCount() {
    initThreeCopies();
    assertTrue(getMultiset().removeAll(singleton(e0())));
    assertEmpty(getMultiset());
  }

  @CollectionSize.Require(SEVERAL)
  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testRetainAllIgnoresCount() {

  }

  @CollectionSize.Require(SEVERAL)
  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testRemoveAllIgnoresCount() {
    initThreeCopies();
    assertTrue(getMultiset().removeAll(singleton(e0())));
    assertEmpty(getMultiset());
  }

  @CollectionSize.Require(SEVERAL)
  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testRetainAllIgnoresCount() {

///

## Separating tests { #separating-tests }

In a real application, you probably would have your tests in a different file.

And your **FastAPI** application might also be composed of several files/modules, etc.

### **FastAPI** app file { #fastapi-app-file }

Let's say you have a file structure as described in [Bigger Applications](bigger-applications.md){.internal-link target=_blank}:

```
.
├── app