Fix missing test deps

Author: goanpeca

binder/environment.yml

@@ -26,6 +26,7 @@ dependencies:
 - pygments >=2.0
 - pylint >=0.25
 - pyqt <5.13
+- pyyaml
 - python-language-server >=0.31.2,<0.32.0
 - pyxdg >=0.26
 - pyzmq >=17

requirements/tests.txt

@@ -2,19 +2,20 @@
 # So to get performant launches on mybinder.org, we have copied
 # the contents of this file to binder/environment.yml. If you
 # make changes here, please copy them over there too.
+coverage <5.0
+cython
+flaky
+matplotlib
+mock
+pandas
+pillow
 pytest <5.0
-pytest-mock
 pytest-cov
-pytest-qt
-pytest-ordering
-pytest-lazy-fixture
 pytest-faulthandler <2.0
-mock
-pandas
+pytest-lazy-fixture
+pytest-mock
+pytest-ordering
+pytest-qt
+pyyaml
 scipy
 sympy
-pillow
-matplotlib
-cython
-flaky
-coverage <5.0