diff --git a/tests/commands/test_ci.py b/tests/commands/test_ci.py
index 8a597413..0f7aceed 100644
--- a/tests/commands/test_ci.py
+++ b/tests/commands/test_ci.py
@@ -24,7 +24,7 @@ def test_ci_empty(clirunner):
     assert "Invalid value: Missing argument 'src'" in result.output
 
 
-def test_ci_boards(clirunner, validate_cliresult, isolated_pio_core):
+def test_ci_boards(clirunner, validate_cliresult):
     result = clirunner.invoke(
         cmd_ci,
         [
@@ -38,7 +38,7 @@ def test_ci_boards(clirunner, validate_cliresult, isolated_pio_core):
     validate_cliresult(result)
 
 
-def test_ci_build_dir(clirunner, tmpdir_factory, validate_cliresult, isolated_pio_core):
+def test_ci_build_dir(clirunner, tmpdir_factory, validate_cliresult):
     build_dir = str(tmpdir_factory.mktemp("ci_build_dir"))
     result = clirunner.invoke(
         cmd_ci,
@@ -54,9 +54,7 @@ def test_ci_build_dir(clirunner, tmpdir_factory, validate_cliresult, isolated_pi
     assert not isfile(join(build_dir, "platformio.ini"))
 
 
-def test_ci_keep_build_dir(
-    clirunner, tmpdir_factory, validate_cliresult, isolated_pio_core
-):
+def test_ci_keep_build_dir(clirunner, tmpdir_factory, validate_cliresult):
     build_dir = str(tmpdir_factory.mktemp("ci_build_dir"))
     result = clirunner.invoke(
         cmd_ci,
@@ -90,7 +88,7 @@ def test_ci_keep_build_dir(
     assert "board: metro" in result.output
 
 
-def test_ci_project_conf(clirunner, validate_cliresult, isolated_pio_core):
+def test_ci_project_conf(clirunner, validate_cliresult):
     project_dir = join("examples", "wiring-blink")
     result = clirunner.invoke(
         cmd_ci,
@@ -104,9 +102,7 @@ def test_ci_project_conf(clirunner, validate_cliresult, isolated_pio_core):
     assert "uno" in result.output
 
 
-def test_ci_lib_and_board(
-    clirunner, tmpdir_factory, validate_cliresult, isolated_pio_core
-):
+def test_ci_lib_and_board(clirunner, tmpdir_factory, validate_cliresult):
     storage_dir = str(tmpdir_factory.mktemp("lib"))
     result = clirunner.invoke(
         cmd_lib, ["--storage-dir", storage_dir, "install", "1@2.3.2"]
diff --git a/tests/commands/test_test.py b/tests/commands/test_test.py
index 2b6dc348..16e0556c 100644
--- a/tests/commands/test_test.py
+++ b/tests/commands/test_test.py
@@ -13,16 +13,14 @@
 # limitations under the License.
 
 import os
-import sys
 
 import pytest
 
 from platformio import util
 from platformio.commands.test.command import cli as cmd_test
-from platformio.compat import WINDOWS
 
 
-def test_local_env(isolated_pio_core):
+def test_local_env():
     result = util.exec_command(
         [
             "platformio",
@@ -40,7 +38,7 @@ def test_local_env(isolated_pio_core):
     ]
 
 
-def test_multiple_env_build(clirunner, validate_cliresult, isolated_pio_core, tmpdir):
+def test_multiple_env_build(clirunner, validate_cliresult, tmpdir):
 
     project_dir = tmpdir.mkdir("project")
     project_dir.join("platformio.ini").write(
@@ -85,9 +83,7 @@ void loop() {}
     assert "Multiple ways to build" not in result.output
 
 
-def test_setup_teardown_are_compilable(
-    clirunner, validate_cliresult, isolated_pio_core, tmpdir
-):
+def test_setup_teardown_are_compilable(clirunner, validate_cliresult, tmpdir):
 
     project_dir = tmpdir.mkdir("project")
     project_dir.join("platformio.ini").write(
diff --git a/tests/conftest.py b/tests/conftest.py
index 438ced13..56a59cbd 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -36,16 +36,9 @@ def validate_cliresult():
     return decorator
 
 
-@pytest.fixture(scope="module")
-def clirunner():
-    return CliRunner()
-
-
-@pytest.fixture(scope="module")
-def isolated_pio_core(request, tmpdir_factory):
-    core_dir = tmpdir_factory.mktemp(".platformio")
+@pytest.fixture(scope="session")
+def clirunner(request):
     backup_env_vars = {
-        "PLATFORMIO_CORE_DIR": {"new": str(core_dir)},
         "PLATFORMIO_WORKSPACE_DIR": {"new": None},
     }
     for key, item in backup_env_vars.items():
@@ -62,6 +55,19 @@ def isolated_pio_core(request, tmpdir_factory):
             elif key in os.environ:
                 del os.environ[key]
 
+    request.addfinalizer(fin)
+
+    return CliRunner()
+
+
+@pytest.fixture(scope="module")
+def isolated_pio_core(request, tmpdir_factory):
+    core_dir = tmpdir_factory.mktemp(".platformio")
+    os.environ["PLATFORMIO_CORE_DIR"] = str(core_dir)
+
+    def fin():
+        del os.environ["PLATFORMIO_CORE_DIR"]
+
     request.addfinalizer(fin)
     return core_dir
 
diff --git a/tests/test_builder.py b/tests/test_builder.py
index dd0fe1f2..f220e50c 100644
--- a/tests/test_builder.py
+++ b/tests/test_builder.py
@@ -15,7 +15,7 @@
 from platformio.commands.run.command import cli as cmd_run
 
 
-def test_build_flags(clirunner, isolated_pio_core, validate_cliresult, tmpdir):
+def test_build_flags(clirunner, validate_cliresult, tmpdir):
     build_flags = [
         ("-D TEST_INT=13", "-DTEST_INT=13"),
         ("-DTEST_SINGLE_MACRO", "-DTEST_SINGLE_MACRO"),
diff --git a/tests/test_ino2cpp.py b/tests/test_ino2cpp.py
index af91da8d..d1434df7 100644
--- a/tests/test_ino2cpp.py
+++ b/tests/test_ino2cpp.py
@@ -31,12 +31,12 @@ def pytest_generate_tests(metafunc):
     metafunc.parametrize("piotest_dir", test_dirs)
 
 
-def test_example(clirunner, isolated_pio_core, validate_cliresult, piotest_dir):
+def test_example(clirunner, validate_cliresult, piotest_dir):
     result = clirunner.invoke(cmd_ci, [piotest_dir, "-b", "uno"])
     validate_cliresult(result)
 
 
-def test_warning_line(clirunner, isolated_pio_core, validate_cliresult):
+def test_warning_line(clirunner, validate_cliresult):
     result = clirunner.invoke(cmd_ci, [join(INOTEST_DIR, "basic"), "-b", "uno"])
     validate_cliresult(result)
     assert 'basic.ino:16:14: warning: #warning "Line number is 16"' in result.output