Simplify check_requirements

Assume env var has a path.
Use os.pathsep (not to be confused with os.path.sep) instead of magic string.

Update test to ensure assumption is correct, and check ANT path has been prepended to the path var.

buildozer/targets/android.py

@@ -302,14 +302,13 @@ def check_requirements(self):
             "app", "android.adb_args", "")
         self.adb_args = shlex.split(adb_args)
 
-        # Need to add internally installed ant to path for external tools
-        # like adb to use
-        path = [join(self.apache_ant_dir, 'bin')]
-        if 'PATH' in self.buildozer.environ:
-            path.append(self.buildozer.environ['PATH'])
-        else:
-            path.append(os.environ['PATH'])
-        self.buildozer.environ['PATH'] = ':'.join(path)
+        # Need to add internally-installed ant to path for external tools
+        # (like adb) to use
+        self.buildozer.environ['PATH'] = os.pathsep.join(
+            join(self.apache_ant_dir, 'bin'),
+            self.buildozer.environ['PATH'],
+            )
+
         buildops.checkbin('Git (git)', 'git')
         buildops.checkbin('Cython (cython)', 'cython')
         buildops.checkbin('Java compiler (javac)', self.javac_cmd)

tests/targets/test_android.py

@@ -1,4 +1,5 @@
 import os
+import os.path
 import tempfile
 from io import StringIO
 from unittest import mock
@@ -153,7 +154,7 @@ def test_check_requirements(self):
         assert not hasattr(target_android, "adb_executable")
         assert not hasattr(target_android, "adb_args")
         assert not hasattr(target_android, "javac_cmd")
-        del buildozer.environ["PATH"]
+        assert "PATH" in buildozer.environ
         with patch_buildops_checkbin() as m_checkbin:
             target_android.check_requirements()
         assert m_checkbin.call_args_list == [
@@ -166,7 +167,10 @@ def test_check_requirements(self):
         assert target_android.adb_args == []
         assert target_android.javac_cmd == "javac"
         assert target_android.keytool_cmd == "keytool"
-        assert "PATH" in buildozer.environ
+        assert buildozer.environ["PATH"].starts_with(
+            os.path.join(
+                target_android.apache_ant_dir, "bin")
+        )
 
     def test_check_configuration_tokens(self):
         """Basic tests for the check_configuration_tokens() method."""