diff --git a/.github/workflows/build_secondary_wheels.yml b/.github/workflows/build_secondary_wheels.yml
index 54caba2..f574f2a 100644
--- a/.github/workflows/build_secondary_wheels.yml
+++ b/.github/workflows/build_secondary_wheels.yml
@@ -62,6 +62,12 @@ jobs:
 
       - name: Copy sdist package
         run: cp dist/frozendict-*.tar.gz dist/frozendict.tar.gz
+
+      - name: Prepare system for core dumps
+        run: |
+            sudo mkdir /cores &&
+            sudo chmod 777 /cores &&
+            sudo bash -c 'echo "/cores/%e.%p.%t" > /proc/sys/kernel/core_pattern'
       
       - name: Build wheels
         uses: pypa/cibuildwheel@v2.16.5
@@ -72,6 +78,7 @@ jobs:
           CIBW_SKIP: "*-musllinux_*"
           CIBW_TEST_REQUIRES: pytest
           CIBW_TEST_COMMAND: > 
+            ulimit -c unlimited &&
             python -X faulthandler {package}/test/debug.py && 
             python -X faulthandler -m pytest -p no:faulthandler -s {package}
         with:
@@ -84,3 +91,10 @@ jobs:
         uses: actions/upload-artifact@v3
         with:
           path: dist/*.tar.gz
+
+      - name: Upload core files
+        uses: actions/upload-artifact@v3
+        if: ${{ failure() }}
+        with:
+          name: cores
+          path: /cores
diff --git a/.gitignore b/.gitignore
index c07b4cc..2b5aa86 100644
--- a/.gitignore
+++ b/.gitignore
@@ -32,3 +32,4 @@ test/core.*
 .idea/
 .vs/
 .coverage
+coverage/
diff --git a/mytest.bat b/mytest.bat
index 944f844..ca2e70a 100644
--- a/mytest.bat
+++ b/mytest.bat
@@ -1 +1 @@
-python test/debug.py && pytest
+python test/debug.py && python -X faulthandler -m pytest -p no:faulthandler
diff --git a/mytest.sh b/mytest.sh
index 6887c4e..2339920 100755
--- a/mytest.sh
+++ b/mytest.sh
@@ -1,3 +1,3 @@
 rm test/core.*
 
-./test/debug.py && pytest
+./test/debug.py && python -X faulthandler -m pytest -p no:faulthandler
diff --git a/test/base.py b/test/base.py
index 512ff6f..de7a709 100644
--- a/test/base.py
+++ b/test/base.py
@@ -84,6 +84,10 @@ def fd_dict_2(self):
     def fd_dict_sabina(self):
         return {'Corrado': 'Guzzanti', 'Sabina': 'Guzzanti'}
 
+    @pytest.fixture
+    def fd_dict_none(self):
+        return {'Corrado': None, 'Sabina': None}
+
     @pytest.fixture
     def generator_seq2(self, fd_dict):
         seq2 = list(fd_dict.items())
@@ -117,6 +121,10 @@ def fd2(self, fd_dict_2):
     def fd_sabina(self, fd_dict_sabina):
         return self.FrozendictClass(fd_dict_sabina)
 
+    @pytest.fixture
+    def fromkeys_keys(self):
+        return ["Corrado", "Sabina"]
+
     @pytest.fixture
     def fd_items(self, fd_dict):
         return tuple(fd_dict.items())
diff --git a/test/common.py b/test/common.py
index 9fbacb3..05ef129 100644
--- a/test/common.py
+++ b/test/common.py
@@ -129,6 +129,14 @@ def test_todict(self, fd, fd_dict):
     def test_get(self, fd):
         assert fd.get("Guzzanti") == "Corrado"
 
+    def test_get_bad(self, fd):
+        with pytest.raises(TypeError):
+            fd.get()
+
+    def test_get_bad_2(self, fd):
+        with pytest.raises(TypeError):
+            fd.get(1, 2, 3)
+
     def test_get_fail(self, fd):
         default = object()
         assert fd.get("Brignano", default) is default
@@ -142,11 +150,22 @@ def test_values(self, fd, fd_dict):
     def test_items(self, fd, fd_dict):
         assert tuple(fd.items()) == tuple(fd_dict.items())
 
-    def test_fromkeys(self, fd_sabina):
-        keys = ["Corrado", "Sabina"]
-        f = self.FrozendictClass.fromkeys(keys, "Guzzanti")
+    def test_fromkeys(self, fd_sabina, fromkeys_keys):
+        f = self.FrozendictClass.fromkeys(fromkeys_keys, "Guzzanti")
         assert f == fd_sabina
 
+    def test_fromkeys_bad(self):
+        with pytest.raises(TypeError):
+            f = self.FrozendictClass.fromkeys()
+
+    def test_fromkeys_bad_2(self):
+        with pytest.raises(TypeError):
+            f = self.FrozendictClass.fromkeys(1, 2, 3)
+
+    def test_fromkeys_default(self, fd_dict_none, fromkeys_keys):
+        f = self.FrozendictClass.fromkeys(fromkeys_keys)
+        assert f == fd_dict_none
+    
     def test_fromkeys_dict(self, fd_sabina, fd_dict_sabina):
         f = self.FrozendictClass.fromkeys(fd_dict_sabina, "Guzzanti")
         assert f == fd_sabina
diff --git a/test/debug.py b/test/debug.py
index a686379..d5b10df 100755
--- a/test/debug.py
+++ b/test/debug.py
@@ -1052,6 +1052,50 @@ def func_110():
 functions.append(func_110)
 
 
+@trace()
+def func_111():
+    try:
+        fd_1.get()
+    except TypeError:
+        pass
+
+
+functions.append(func_111)
+
+
+@trace()
+def func_112():
+    try:
+        fd_1.get(1, 2, 3)
+    except TypeError:
+        pass
+
+
+functions.append(func_112)
+
+
+@trace()
+def func_113():
+    try:
+        frozendict.fromkeys()
+    except TypeError:
+        pass
+
+
+functions.append(func_113)
+
+
+@trace()
+def func_114():
+    try:
+        frozendict.fromkeys(1, 2, 3)
+    except TypeError:
+        pass
+
+
+functions.append(func_114)
+
+
 print_sep()
 
 for frozendict_class in (frozendict, F):