Add new help page with tips and tricks for pytest.

doc/development-guidelines/tools/pytest.rst

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+
+########################
+Tips & Tricks for pytest
+########################
+
+-   Run in verbose/no-capture/fail first mode:
+
+    .. prompt::
+
+        pytest -vsx
+
+    v :
+        verbose mode shows the result of each test individually
+
+    s :
+        no-capture shows results or print statements
+
+    x :
+        stop/fail on the first test failure
+
+
+-   Show log messages:
+
+    .. prompt::
+
+        pytest -vsx --log-cli-level DEBUG
+
+    log-cli-level : 
+        controls the log level for the command line at runtime.
+        This allows you to see the log messages as the test runs without the need to fiddle with python logger.
+        You can also use different levels; INFO, WARNING and ERROR.
+
+-   Run a single test file (e.g. the one you are working on):
+
+    .. prompt::
+
+        pytest -vsx tests/test_maintel_disable_m1m3_balance_system.py
+
+
+-   Run a single test from a single file (e.g. debugging a specific error):
+
+    .. prompt::
+
+        pytest -vsx tests/test_maintel_disable_m1m3_balance_system.py -k test_executable
+
+    This will actually do a regular expression match in the test name, so it will actually run everything that matches “test_executable”.