Create the FixtureBuilder class and a simple, happy-path fixture

.env

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+PYTHONPATH=.

Pipfile

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+[[source]]
+name = "pypi"
+url = "https://pypi.org/simple"
+verify_ssl = true
+
+[dev-packages]
+
+[packages]
+certifi = "==2020.6.20"
+cffi = "==1.14.2"
+chardet = "==3.0.4"
+colorama = "==0.4.3"
+cryptography = "==3.3.2"
+idna = "==2.10"
+iso8601 = "==0.1.12"
+pycparser = "==2.20"
+python-dateutil = "==2.8.1"
+requests = "==2.24.0"
+securesystemslib = "==0.20.1"
+six = "==1.15.0"
+tuf = "==0.14.0"
+urllib3 = "==1.25.10"
+PyNaCl = "==1.4.0"
+flake8 = "*"
+
+[requires]
+python_version = "3.9"

build-all.py

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+from fixtures import (
+    simple
+)
+from unittest import mock
+
+
+@mock.patch('time.time', mock.MagicMock(return_value=1577836800))
+def build_all():
+    simple.build()
+
+
+build_all()