Add algorithm for testing Project Euler solutions (TheAlgorithms#2471)

* Add file for testing Project Euler solutions

* Remove the importlib import

* Update project_euler/solution_test.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Small tweaks to project_euler/solution_test.py

* Test Project Euler solutions through Travis

* Improved testing for Project Euler solutions:

- Renamed file so that it isn't picked up by pytest
- Fail fast on validating solutions through Travis CI

* Update validate_solutions.py

* Use namedtuple for input parameters and answer

- Remove logging
- Remove unnecessary checks for PROJECT_EULER_PATH as Travis CI
  picks up the same path

* Fix flake8 errors: line too long

* Small tweaks to validate_solutions.py

* Add all answers & back to using dictionary

* Using pytest for testing Project Euler solutions

- As we want to fail fast on testing solutions, we need to test using
  this script first before we use tests written by the author.
- As pytest stops testing as soon as it receives a traceback, we need to
  use pytest-subtests to tell pytest to test all the iterations for the
  function with given parameters.

* Print error messages in oneline format

* Separated answers into a separate file:

- Add custom print function to print all the error messages at the
  end of all the tests
- Let Travis skip if this failed

Co-authored-by: Christian Clauss <cclauss@me.com>

Author: dhruvmanila

Diff for: .travis.yml

@@ -17,7 +17,9 @@ jobs:
         - mypy --ignore-missing-imports . || true  # https://github.com/python/mypy/issues/7907
         - pytest --doctest-modules --ignore=project_euler/ --durations=10 --cov-report=term-missing:skip-covered --cov=. .
     - name: Project Euler
-      before_script: pip install pytest-cov
+      before_script:
+        - pip install pytest-cov pytest-subtests
+        - pytest --tb=no --no-summary --capture=no project_euler/validate_solutions.py || true  # fail fast on wrong solution
       script:
         - pytest --doctest-modules --durations=10 --cov-report=term-missing:skip-covered --cov=project_euler/ project_euler/
 after_success:

Diff for: project_euler/validate_solutions.py

@@ -0,0 +1,67 @@
+#!/usr/bin/env python3
+import importlib.util
+import json
+import pathlib
+from types import ModuleType
+from typing import Generator
+
+import pytest
+
+PROJECT_EULER_DIR_PATH = pathlib.Path.cwd().joinpath("project_euler")
+PROJECT_EULER_ANSWERS_PATH = PROJECT_EULER_DIR_PATH.joinpath(
+    "project_euler_answers.json"
+)
+
+with open(PROJECT_EULER_ANSWERS_PATH) as file_handle:
+    PROBLEM_ANSWERS = json.load(file_handle)
+
+error_msgs = []
+
+
+def generate_solution_modules(
+    dir_path: pathlib.Path,
+) -> Generator[ModuleType, None, None]:
+    # Iterating over every file or directory
+    for file_path in dir_path.iterdir():
+        if file_path.suffix != ".py" or file_path.name.startswith(("_", "test")):
+            continue
+        # Importing the source file through the given path
+        # https://docs.python.org/3/library/importlib.html#importing-a-source-file-directly
+        spec = importlib.util.spec_from_file_location(file_path.name, str(file_path))
+        module = importlib.util.module_from_spec(spec)
+        spec.loader.exec_module(module)
+        yield module
+
+
+@pytest.mark.parametrize("problem_number, expected", PROBLEM_ANSWERS)
+def test_project_euler(subtests, problem_number: int, expected: str):
+    problem_dir = PROJECT_EULER_DIR_PATH.joinpath(f"problem_{problem_number:02}")
+    # Check if the problem directory exist. If not, then skip.
+    if problem_dir.is_dir():
+        for solution_module in generate_solution_modules(problem_dir):
+            # All the tests in a loop is considered as one test by pytest so, use
+            # subtests to make sure all the subtests are considered as different.
+            with subtests.test(
+                msg=f"Problem {problem_number} tests", solution_module=solution_module
+            ):
+                try:
+                    answer = str(solution_module.solution())
+                    assert answer == expected, f"Expected {expected} but got {answer}"
+                except (AssertionError, AttributeError, TypeError) as err:
+                    error_msgs.append(
+                        f"problem_{problem_number}/{solution_module.__name__}: {err}"
+                    )
+                    raise  # We still want pytest to know that this test failed
+    else:
+        pytest.skip(f"Solution {problem_number} does not exist yet.")
+
+
+# Run this function at the end of all the tests
+# https://stackoverflow.com/a/52873379
+@pytest.fixture(scope="session", autouse=True)
+def custom_print_message(request):
+    def print_error_messages():
+        if error_msgs:
+            print("\n" + "\n".join(error_msgs))
+
+    request.addfinalizer(print_error_messages)