3610 add trace option

changelog/3610.feature.rst

@@ -0,0 +1 @@
+Added the `--trace` option to enter the debugger at the start of a test.

doc/en/usage.rst

@@ -171,6 +171,18 @@ for example::
  >>> sys.last_value
  AssertionError('assert result == "ok"',)
 
+.. _trace-option:
+
+Dropping to PDB_ (Python Debugger) at the start of a test
+----------------------------------------------------------
+
+
+``pytest`` allows one to drop into the PDB_ prompt immediately at the start of each test via a command line option::
+
+ pytest --trace
+
+This will invoke the Python debugger at the start of every test.
+
 .. _breakpoints:
 
 Setting breakpoints

src/_pytest/debugging.py

@@ -5,6 +5,8 @@
 import os
 from doctest import UnexpectedException
 
+from _pytest.config import hookimpl
+
 try:
  from builtins import breakpoint # noqa
 
@@ -28,6 +30,12 @@ def pytest_addoption(parser):
  help="start a custom interactive Python debugger on errors. "
  "For example: --pdbcls=IPython.terminal.debugger:TerminalPdb",
  )
+ group._addoption(
+ "--trace",
+ dest="trace",
+ action="store_true",
+ help="Immediately break when running each test.",
+ )
 
 
 def pytest_configure(config):
@@ -38,6 +46,8 @@ def pytest_configure(config):
  else:
  pdb_cls = pdb.Pdb
 
+ if config.getvalue("trace"):
+ config.pluginmanager.register(PdbTrace(), "pdbtrace")
  if config.getvalue("usepdb"):
  config.pluginmanager.register(PdbInvoke(), "pdbinvoke")
 
@@ -71,7 +81,7 @@ class pytestPDB(object):
  _pdb_cls = pdb.Pdb
 
  @classmethod
- def set_trace(cls):
+ def set_trace(cls, set_break=True):
  """ invoke PDB set_trace debugging, dropping any IO capturing. """
  import _pytest.config
 
@@ -84,7 +94,8 @@ def set_trace(cls):
  tw.line()
  tw.sep(">", "PDB set_trace (IO-capturing turned off)")
  cls._pluginmanager.hook.pytest_enter_pdb(config=cls._config)
- cls._pdb_cls().set_trace(frame)
+ if set_break:
+ cls._pdb_cls().set_trace(frame)
 
 
 class PdbInvoke(object):
@@ -104,6 +115,30 @@ def pytest_internalerror(self, excrepr, excinfo):
  post_mortem(tb)
 
 
+class PdbTrace(object):
+ @hookimpl(hookwrapper=True)
+ def pytest_pyfunc_call(self, pyfuncitem):
+ _test_pytest_function(pyfuncitem)
+ yield
+
+
+def _test_pytest_function(pyfuncitem):
+ pytestPDB.set_trace(set_break=False)
+ testfunction = pyfuncitem.obj
+ pyfuncitem.obj = pdb.runcall
+ if pyfuncitem._isyieldedfunction():
+ arg_list = list(pyfuncitem._args)
+ arg_list.insert(0, testfunction)
+ pyfuncitem._args = tuple(arg_list)
+ else:
+ if "func" in pyfuncitem._fixtureinfo.argnames:
+ raise ValueError("--trace can't be used with a fixture named func!")
+ pyfuncitem.funcargs["func"] = testfunction
+ new_list = list(pyfuncitem._fixtureinfo.argnames)
+ new_list.append("func")
+ pyfuncitem._fixtureinfo.argnames = tuple(new_list)
+
+
 def _enter_pdb(node, excinfo, rep):
  # XXX we re-use the TerminalReporter's terminalwriter
  # because this seems to avoid some encoding related troubles

testing/test_pdb.py

@@ -696,3 +696,40 @@ def test_1():
  assert "1 failed" in rest
  assert "reading from stdin while output" not in rest
  TestPDB.flush(child)
+
+
+class TestTraceOption:
+ def test_trace_sets_breakpoint(self, testdir):
+ p1 = testdir.makepyfile(
+ """
+ def test_1():
+ assert True
+ """
+ )
+ child = testdir.spawn_pytest("--trace " + str(p1))
+ child.expect("test_1")
+ child.expect("(Pdb)")
+ child.sendeof()
+ rest = child.read().decode("utf8")
+ assert "1 passed" in rest
+ assert "reading from stdin while output" not in rest
+ TestPDB.flush(child)
+
+ def test_trace_against_yield_test(self, testdir):
+ p1 = testdir.makepyfile(
+ """
+ def is_equal(a, b):
+ assert a == b
+
+ def test_1():
+ yield is_equal, 1, 1
+ """
+ )
+ child = testdir.spawn_pytest("--trace " + str(p1))
+ child.expect("is_equal")
+ child.expect("(Pdb)")
+ child.sendeof()
+ rest = child.read().decode("utf8")
+ assert "1 passed" in rest
+ assert "reading from stdin while output" not in rest
+ TestPDB.flush(child)