check_preimported=True controls whether coverage checks pre-imported files when starting

5 files changed, 15 insertions, 12 deletions

diff --git a/coverage/cmdline.py b/coverage/cmdline.py
index 7b86054e..04cf8e89 100644
--- a/coverage/cmdline.py
+++ b/coverage/cmdline.py
@@ -475,6 +475,7 @@ class CoverageScript(object):
             include=include,
             debug=debug,
             concurrency=options.concurrency,
+            check_preimported=True,
             )
 
         if options.action == "debug":
diff --git a/coverage/control.py b/coverage/control.py
index 77efe28b..55c031ae 100644
--- a/coverage/control.py
+++ b/coverage/control.py
@@ -53,15 +53,12 @@ class Coverage(object):
         cov.html_report(directory='covhtml')
 
     """
-    # A global to know if we have ever checked for files imported before
-    # coverage has been started.
-    _checked_preimported = False
 
     def __init__(
         self, data_file=None, data_suffix=None, cover_pylib=None,
         auto_data=False, timid=None, branch=None, config_file=True,
         source=None, omit=None, include=None, debug=None,
-        concurrency=None,
+        concurrency=None, check_preimported=False,
     ):
         """
         `data_file` is the base name of the data file to use, defaulting to
@@ -115,12 +112,20 @@ class Coverage(object):
         "eventlet", "gevent", "multiprocessing", or "thread" (the default).
         This can also be a list of these strings.
 
+        If `check_preimported` is true, then when coverage is started, the
+        aleady-imported files will be checked to see if they should be measured
+        by coverage.  Importing measured files before coverage is started can
+        mean that code is missed.
+
         .. versionadded:: 4.0
             The `concurrency` parameter.
 
         .. versionadded:: 4.2
             The `concurrency` parameter can now be a list of strings.
 
+        .. versionadded:: 4.6
+            The `check_preimported` parameter.
+
         """
         # Build our configuration from a number of sources.
         self.config_file, self.config = read_coverage_config(
@@ -141,7 +146,7 @@ class Coverage(object):
         # Is it ok for no data to be collected?
         self._warn_no_data = True
         self._warn_unimported_source = True
-        self._warn_preimported_source = True
+        self._warn_preimported_source = check_preimported
 
         # A record of all the warnings that have been issued.
         self._warnings = []
@@ -414,8 +419,8 @@ class Coverage(object):
             self.load()
 
         # See if we think some code that would eventually be measured has already been imported.
-        if not Coverage._checked_preimported and self._warn_preimported_source:
-            Coverage._checked_preimported = self._inorout.warn_already_imported_files()
+        if self._warn_preimported_source:
+            self._inorout.warn_already_imported_files()
 
         self.collector.start()
         self._started = True
diff --git a/coverage/inorout.py b/coverage/inorout.py
index 640b4e6f..53ed8ea9 100644
--- a/coverage/inorout.py
+++ b/coverage/inorout.py
@@ -354,9 +354,6 @@ class InOrOut(object):
                     self.warn(msg, slug="already-imported")
                     warned.add(filename)
 
-            return True
-        return False
-
     def warn_unimported_source(self):
         for pkg in self.source_pkgs_unmatched:
             self.warn_about_unmeasured_code(pkg)
diff --git a/tests/test_cmdline.py b/tests/test_cmdline.py
index 1b7c6653..66fcec3a 100644
--- a/tests/test_cmdline.py
+++ b/tests/test_cmdline.py
@@ -33,7 +33,7 @@ class BaseCmdLineTest(CoverageTest):
     defaults.Coverage(
         cover_pylib=None, data_suffix=None, timid=None, branch=None,
         config_file=True, source=None, include=None, omit=None, debug=None,
-        concurrency=None,
+        concurrency=None, check_preimported=True,
     )
     defaults.annotate(
         directory=None, ignore_errors=None, include=None, omit=None, morfs=[],
diff --git a/tests/test_process.py b/tests/test_process.py
index 9d4aa56e..fb08562f 100644
--- a/tests/test_process.py
+++ b/tests/test_process.py
@@ -589,7 +589,7 @@ class ProcessTest(CoverageTest):
         self.make_file("hello.py", """\
             import goodbye
             import coverage
-            cov = coverage.Coverage(include=["good*"])
+            cov = coverage.Coverage(include=["good*"], check_preimported=True)
             cov.start()
             print(goodbye.f())
             cov.stop()