examples: use pip 21.3

examples/maturin-starter/requirements-dev.txt

@@ -1 +1,2 @@
 pytest>=3.5.0
+pip>=21.3

examples/maturin-starter/tox.ini

@@ -4,11 +4,7 @@ skipsdist = true
 
 [testenv]
 description = Run the unit tests under {basepython}
-deps =
-    pip>=21.1 # for in-tree-build
-    -rrequirements-dev.txt
+deps = -rrequirements-dev.txt
 commands =
-    # --use-feature=in-tree-build is necessary because this example is inside
-    # the PyO3 repo.
-    python -m pip install . --use-feature=in-tree-build
+    python -m pip install .
     pytest {posargs}

examples/pyo3-benchmarks/requirements-dev.txt

@@ -1,3 +1,4 @@
 pytest>=3.5.0
 setuptools-rust>=0.10.2
 pytest-benchmark~=3.2
+pip>=21.3

examples/pyo3-benchmarks/tox.ini

@@ -1,10 +1,5 @@
-[tox]
-# can't install from sdist because local pyo3 repo can't be included in the sdist
-skipsdist = true
-
 [testenv]
+usedevelop = True
 description = Run the unit tests under {basepython}
 deps = -rrequirements-dev.txt
-commands =
-    python setup.py install
-    pytest --benchmark-sort=name {posargs}
+commands = pytest --benchmark-sort=name {posargs}

examples/pyo3-pytests/requirements-dev.txt

@@ -1,3 +1,4 @@
 hypothesis>=3.55
 pytest>=3.5.0
 psutil>=5.6
+pip>=21.3

examples/pyo3-pytests/tox.ini

@@ -4,11 +4,7 @@ skipsdist = true
 
 [testenv]
 description = Run the unit tests under {basepython}
-deps =
-    pip>=21.1 # for in-tree-build
-    -rrequirements-dev.txt
+deps = -rrequirements-dev.txt
 commands =
-    # --use-feature=in-tree-build is necessary because this example is inside
-    # the PyO3 repo.
-    python -m pip install . --use-feature=in-tree-build
+    python -m pip install .
     pytest {posargs}

examples/setuptools-rust-starter/requirements-dev.txt

@@ -1,2 +1,3 @@
 pytest>=3.5.0
 setuptools_rust~=0.11.0
+pip>=21.3

examples/setuptools-rust-starter/tox.ini

@@ -1,10 +1,5 @@
-[tox]
-# can't install from sdist because local pyo3 repo can't be included in the sdist
-skipsdist = true
-
 [testenv]
+usedevelop = true
 description = Run the unit tests under {basepython}
 deps = -rrequirements-dev.txt
-commands =
-    python setup.py install
-    pytest {posargs}
+commands = pytest {posargs}

examples/word-count/tox.ini

@@ -1,10 +1,5 @@
-[tox]
-# can't install from sdist because local pyo3 repo can't be included in the sdist
-skipsdist=true
-
 [testenv]
+usedevelop = true
 description = Run the unit tests under {basepython}
 deps = -rrequirements-dev.txt
-commands =
-    python setup.py install
-    pytest {posargs}
+commands = pytest {posargs}