Fix tests for file_transfer and perceptron.py

Author: cclauss

.travis.yml

@@ -28,9 +28,9 @@ script:
   - scripts/validate_filenames.py  # no uppercase, no spaces, in a directory
   - mypy --ignore-missing-imports .
   - pytest . --doctest-modules
-      --ignore=machine_learning/linear_regression.py
-      --ignore=machine_learning/random_forest_classification/random_forest_classification.py
-      --ignore=machine_learning/random_forest_regression/random_forest_regression.py
+      #--ignore=machine_learning/linear_regression.py
+      #--ignore=machine_learning/random_forest_classification/random_forest_classification.py
+      #--ignore=machine_learning/random_forest_regression/random_forest_regression.py
 after_success:
   - scripts/build_directory_md.py > DIRECTORY.md
   - cat DIRECTORY.md