diff --git a/mypy/test/testcheck.py b/mypy/test/testcheck.py
index 77c820e51fa6..d6d051b1cb9c 100644
--- a/mypy/test/testcheck.py
+++ b/mypy/test/testcheck.py
@@ -1,6 +1,6 @@
 """Type checker test cases"""
 
-import os.path
+import os
 import re
 import shutil
 import sys
@@ -154,6 +154,8 @@ def run_case_once(self, testcase: DataDrivenTestCase, incremental: int = 0) -> N
             options.strict_optional = True
         if incremental:
             options.incremental = True
+        else:
+            options.cache_dir = os.devnull  # Dont waste time writing cache
 
         sources = []
         for module_name, program_path, program_text in module_data:
diff --git a/mypy/test/testdeps.py b/mypy/test/testdeps.py
index e1ee2b97e3e5..bfbf1db13391 100644
--- a/mypy/test/testdeps.py
+++ b/mypy/test/testdeps.py
@@ -1,6 +1,6 @@
 """Test cases for generating node-level dependencies (for fine-grained incremental checking)"""
 
-import os.path
+import os
 from typing import List, Tuple, Dict
 
 from mypy import build
@@ -54,6 +54,7 @@ def build(self, source: str) -> Tuple[List[str],
         options = Options()
         options.use_builtins_fixtures = True
         options.show_traceback = True
+        options.cache_dir = os.devnull
         try:
             result = build.build(sources=[BuildSource('main', None, source)],
                                  options=options,
diff --git a/mypy/test/testdiff.py b/mypy/test/testdiff.py
index f379a3735ce7..e24575b33d68 100644
--- a/mypy/test/testdiff.py
+++ b/mypy/test/testdiff.py
@@ -1,6 +1,6 @@
 """Test cases for AST diff (used for fine-grained incremental checking)"""
 
-import os.path
+import os
 from typing import List, Tuple, Dict
 
 from mypy import build
@@ -62,6 +62,7 @@ def build(self, source: str) -> Tuple[List[str], Dict[str, MypyFile]]:
         options = Options()
         options.use_builtins_fixtures = True
         options.show_traceback = True
+        options.cache_dir = os.devnull
         try:
             result = build.build(sources=[BuildSource('main', None, source)],
                                  options=options,
diff --git a/mypy/test/testfinegrained.py b/mypy/test/testfinegrained.py
index 21afc8572b44..fff2e18d26ba 100644
--- a/mypy/test/testfinegrained.py
+++ b/mypy/test/testfinegrained.py
@@ -7,7 +7,7 @@
 information.
 """
 
-import os.path
+import os
 import re
 import shutil
 from typing import List, Tuple, Dict
@@ -83,6 +83,7 @@ def build(self, source: str) -> Tuple[List[str], BuildManager, Graph]:
         options = Options()
         options.use_builtins_fixtures = True
         options.show_traceback = True
+        options.cache_dir = os.devnull
         try:
             result = build.build(sources=[BuildSource('main', None, source)],
                                  options=options,
diff --git a/mypy/test/testmerge.py b/mypy/test/testmerge.py
index 6802e3431091..9807098877cf 100644
--- a/mypy/test/testmerge.py
+++ b/mypy/test/testmerge.py
@@ -1,6 +1,6 @@
 """Test cases for AST merge (used for fine-grained incremental checking)"""
 
-import os.path
+import os
 import shutil
 from typing import List, Tuple, Dict
 
@@ -100,6 +100,7 @@ def build(self, source: str) -> Tuple[List[str], BuildManager, Dict[str, State]]
         options = Options()
         options.use_builtins_fixtures = True
         options.show_traceback = True
+        options.cache_dir = os.devnull
         try:
             result = build.build(sources=[BuildSource('main', None, source)],
                                  options=options,