Avoid importing coverage for test runs that don't need it

src/pytest_cov/engine.py

@@ -5,9 +5,6 @@
 import socket
 import sys
 
-import coverage
-from coverage.data import CoverageData
-
 from .embed import cleanup
 from .compat import StringIO, workeroutput, workerinput
 
@@ -93,6 +90,10 @@ def summary(self, stream):
         if not self.cov_report:
             return self.cov.report(show_missing=True, ignore_errors=True, file=_NullFile)
 
+        # import coverage lazily here to avoid importing
+        # it for unit tests that don't need it
+        import coverage
+
         # Output coverage section header.
         if len(self.node_descs) == 1:
             self.sep(stream, '-', 'coverage: %s' % ''.join(self.node_descs))
@@ -152,6 +153,10 @@ class Central(CovController):
     def start(self):
         cleanup()
 
+        # import coverage lazily here to avoid importing
+        # it for unit tests that don't need it
+        import coverage
+
         self.cov = coverage.Coverage(source=self.cov_source,
                                      branch=self.cov_branch,
                                      config_file=self.cov_config)
@@ -190,6 +195,10 @@ class DistMaster(CovController):
     def start(self):
         cleanup()
 
+        # import coverage lazily here to avoid importing
+        # it for unit tests that don't need it
+        import coverage
+
         # Ensure coverage rc file rsynced if appropriate.
         if self.cov_config and os.path.exists(self.cov_config):
             self.config.option.rsyncdir.append(self.cov_config)
@@ -236,11 +245,17 @@ def testnodedown(self, node, error):
                 output['cov_worker_node_id']
                 )
 
+            # import coverage lazily here to avoid importing
+            # it for unit tests that don't need it
+            import coverage
+            from coverage.data import CoverageData
+
             cov = coverage.Coverage(source=self.cov_source,
                                     branch=self.cov_branch,
                                     data_suffix=data_suffix,
                                     config_file=self.cov_config)
             cov.start()
+
             data = CoverageData()
             data.read_fileobj(StringIO(output['cov_worker_data']))
             cov.data.update(data)
@@ -272,6 +287,10 @@ class DistWorker(CovController):
     def start(self):
         cleanup()
 
+        # import coverage lazily here to avoid importing
+        # it for unit tests that don't need it
+        import coverage
+
         # Determine whether we are collocated with master.
         self.is_collocated = (socket.gethostname() == workerinput(self.config)['cov_master_host'] and
                               self.topdir == workerinput(self.config)['cov_master_topdir'])

src/pytest_cov/plugin.py

@@ -4,7 +4,6 @@
 import warnings
 
 import pytest
-from coverage.misc import CoverageException
 
 from . import compat
 from . import embed
@@ -239,6 +238,11 @@ def pytest_runtestloop(self, session):
             self.cov_controller.finish()
 
         if not self._is_worker(session) and self._should_report():
+
+            # import coverage lazily here to avoid importing
+            # it for unit tests that don't need it
+            from coverage.misc import CoverageException
+
             try:
                 self.cov_total = self.cov_controller.summary(self.cov_report)
             except CoverageException as exc: