Improve exception handling in subprocess setup. Fix broken output han…

…dling in #144. Add a test for this.

src/pytest-cov.embed

@@ -2,9 +2,12 @@ if 'COV_CORE_SOURCE' in os.environ:
     try:
         from pytest_cov.embed import init
         init()
-    except ImportError as exc:
+    except Exception as exc:
         sys.stderr.write(
-            "Failed to setup coverage."
-            "Sources: {[COV_CORE_SOURCE]!r}"
-            "Config: {[COV_CORE_CONFIG]!r}"
-            "Exception: {!r}\n".format(os.environ, exc))
+            "pytest-cov: Failed to setup subprocess coverage. "
+            "Environ: {0!r} "
+            "Exception: {1!r}\n".format(
+                dict((k, v) for k, v in os.environ.items() if k.startswith('COV_CORE')),
+                exc
+            )
+        )

src/pytest-cov.pth

@@ -1 +1 @@
-import os, sys;exec('if \'COV_CORE_SOURCE\' in os.environ:\n try:\n  from pytest_cov.embed import init\n  init()\n except ImportError as exc:\n  sys.stderr.write(\n   "Failed to setup coverage."\n   "Sources: {[COV_CORE_SOURCE]!r}"\n   "Config: {[COV_CORE_CONFIG]!r}"\n   "Exception: {!r}\\n".format(os.environ, exc))\n')
+import os, sys;exec('if \'COV_CORE_SOURCE\' in os.environ:\n try:\n  from pytest_cov.embed import init\n  init()\n except Exception as exc:\n  sys.stderr.write(\n   "pytest-cov: Failed to setup subprocess coverage. "\n   "Environ: {0!r} "\n   "Exception: {1!r}\\n".format(\n    dict((k, v) for k, v in os.environ.items() if k.startswith(\'COV_CORE\')),\n    exc\n   )\n  )\n')

tests/test_pytest_cov.py

@@ -3,6 +3,7 @@
 import subprocess
 import sys
 from distutils.version import StrictVersion
+from io import StringIO
 from itertools import chain
 
 import coverage
@@ -1169,3 +1170,25 @@ def test_do_not_append_coverage(testdir, opts):
         'test_1* 0%',
         'test_2* %s*' % SCRIPT2_RESULT,
     ])
+
+
+def test_pth_failure(monkeypatch):
+    with open('src/pytest-cov.pth') as fh:
+        payload = fh.read()
+
+    class SpecificError(Exception):
+        pass
+
+    def bad_init():
+        raise SpecificError()
+
+    buff = StringIO()
+
+    from pytest_cov import embed
+
+    monkeypatch.setattr(embed, 'init', bad_init)
+    monkeypatch.setattr(sys, 'stderr', buff)
+    monkeypatch.setitem(os.environ, 'COV_CORE_SOURCE', 'foobar')
+    exec(payload)
+    assert buff.getvalue() == '''pytest-cov: Failed to setup subprocess coverage. Environ: {'COV_CORE_SOURCE': 'foobar'} Exception: SpecificError()
+'''