Clean autogenerated files before running tests // Resolve #3523

Fixes possible conflicts between auxiliary test transport files when
project contains multiple environments with different platforms

tests/commands/test_test.py

@@ -17,6 +17,7 @@ from os.path import join
 import pytest
 
 from platformio import util
+from platformio.commands.test.command import cli as cmd_test
 
 
 def test_local_env():
@@ -31,7 +32,49 @@ def test_local_env():
         ]
     )
     if result["returncode"] != 1:
-        pytest.fail(result)
+        pytest.fail(str(result))
     assert all([s in result["err"] for s in ("PASSED", "IGNORED", "FAILED")]), result[
         "out"
     ]
+
+
+def test_multiple_env_build(clirunner, validate_cliresult, tmpdir):
+
+    project_dir = tmpdir.mkdir("project")
+    project_dir.join("platformio.ini").write(
+        """
+[env:teensy31]
+platform = teensy
+framework = mbed
+board = teensy31
+
+[env:native]
+platform = native
+
+[env:espressif32]
+platform = espressif32
+framework = arduino
+board = esp32dev
+"""
+    )
+
+    project_dir.mkdir("test").join("test_main.cpp").write(
+        """
+#ifdef ARDUINO
+void setup() {}
+void loop() {}
+#else
+int main() {
+    UNITY_BEGIN();
+    UNITY_END();
+}
+#endif
+"""
+    )
+
+    result = clirunner.invoke(
+        cmd_test, ["-d", str(project_dir), "--without-testing", "--without-uploading"],
+    )
+
+    validate_cliresult(result)
+    assert "Multiple ways to build" not in result.output