Fix --append trying to make a new file. #392

2 files changed, 36 insertions, 9 deletions

diff --git a/tests/test_cmdline.py b/tests/test_cmdline.py
index 3baa2626..4c54088a 100644
--- a/tests/test_cmdline.py
+++ b/tests/test_cmdline.py
@@ -63,30 +63,33 @@ class BaseCmdLineTest(CoverageTest):
 
         return mk
 
-    def mock_command_line(self, args):
+    def mock_command_line(self, args, path_exists=None):
         """Run `args` through the command line, with a Mock.
 
         Returns the Mock it used and the status code returned.
 
         """
         m = self.model_object()
+        m.path_exists.return_value = path_exists
+
         ret = coverage.cmdline.CoverageScript(
             _covpkg=m, _run_python_file=m.run_python_file,
-            _run_python_module=m.run_python_module, _help_fn=m.help_fn
+            _run_python_module=m.run_python_module, _help_fn=m.help_fn,
+            _path_exists=m.path_exists,
             ).command_line(shlex.split(args))
+
         return m, ret
 
-    def cmd_executes(self, args, code, ret=OK):
+    def cmd_executes(self, args, code, ret=OK, path_exists=None):
         """Assert that the `args` end up executing the sequence in `code`."""
-        m1, r1 = self.mock_command_line(args)
-        self.assertEqual(
-            r1, ret, "Wrong status: got %s, wanted %s" % (r1, ret)
-        )
+        m1, r1 = self.mock_command_line(args, path_exists=path_exists)
+        self.assertEqual(r1, ret, "Wrong status: got %r, wanted %r" % (r1, ret))
 
         # Remove all indentation, and change ".foo()" to "m2.foo()".
         code = re.sub(r"(?m)^\s+", "", code)
         code = re.sub(r"(?m)^\.", "m2.", code)
         m2 = self.model_object()
+        m2.path_exists.return_value = path_exists
         code_obj = compile(code, "<code>", "exec")
         eval(code_obj, globals(), { 'm2': m2 })     # pylint: disable=eval-used
 
@@ -351,15 +354,25 @@ class CmdLineTest(BaseCmdLineTest):
             .stop()
             .save()
             """)
-        # run -a calls coverage.load first without erasing.
+        # run -a combines with an existing data file before saving.
         self.cmd_executes("run -a foo.py", """\
             .coverage()
             .start()
             .run_python_file('foo.py', ['foo.py'])
             .stop()
+            .path_exists('.coverage')
             .combine(data_paths=['.coverage'])
             .save()
-            """)
+            """, path_exists=True)
+        # run -a doesn't combine anything if the data file doesn't exist.
+        self.cmd_executes("run -a foo.py", """\
+            .coverage()
+            .start()
+            .run_python_file('foo.py', ['foo.py'])
+            .stop()
+            .path_exists('.coverage')
+            .save()
+            """, path_exists=False)
         # --timid sets a flag, and program arguments get passed through.
         self.cmd_executes("run --timid foo.py abc 123", """\
             .coverage(timid=True)
diff --git a/tests/test_process.py b/tests/test_process.py
index fcd88827..9bd72119 100644
--- a/tests/test_process.py
+++ b/tests/test_process.py
@@ -168,6 +168,20 @@ class ProcessTest(CoverageTest):
         data.read_file(".mycovdata")
         self.assertEqual(data.line_counts()['b_or_c.py'], 7)
 
+    def test_append_can_create_a_data_file(self):
+        self.make_b_or_c_py()
+
+        out = self.run_command("coverage run --append b_or_c.py b")
+        self.assertEqual(out, 'done\n')
+        self.assert_exists(".coverage")
+        self.assertEqual(self.number_of_data_files(), 1)
+
+        # Read the coverage file and see that b_or_c.py has only 6 lines
+        # executed.
+        data = coverage.CoverageData()
+        data.read_file(".coverage")
+        self.assertEqual(data.line_counts()['b_or_c.py'], 6)
+
     def test_combine_with_rc(self):
         self.make_b_or_c_py()