Merge pull request #3647 from jeffreyrack/3610-add-trace-option

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 sys
 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 @@ class pytestPDB(object):
             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 @@ class PdbInvoke(object):
         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 @@ class TestDebuggingBreakpoints(object):
         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)