diff --git a/pandas/tests/frame/methods/test_equals.py b/pandas/tests/frame/methods/test_equals.py
index dddd6c6d2eaf2..beec3e965d542 100644
--- a/pandas/tests/frame/methods/test_equals.py
+++ b/pandas/tests/frame/methods/test_equals.py
@@ -36,7 +36,8 @@ def test_equals(self):
         df1["start"] = date_range("2000-1-1", periods=10, freq="T")
         df1["end"] = date_range("2000-1-1", periods=10, freq="D")
         df1["diff"] = df1["end"] - df1["start"]
-        df1["bool"] = np.arange(10) % 3 == 0
+        # Explicitly cast to object, to avoid implicit cast when setting np.nan
+        df1["bool"] = (np.arange(10) % 3 == 0).astype(object)
         df1.loc[::2] = np.nan
         df2 = df1.copy()
         assert df1["text"].equals(df2["text"])
diff --git a/pandas/tests/frame/test_query_eval.py b/pandas/tests/frame/test_query_eval.py
index e81837898c927..159dab04e7da6 100644
--- a/pandas/tests/frame/test_query_eval.py
+++ b/pandas/tests/frame/test_query_eval.py
@@ -448,7 +448,8 @@ def test_date_index_query(self):
     def test_date_index_query_with_NaT(self):
         engine, parser = self.engine, self.parser
         n = 10
-        df = DataFrame(np.random.randn(n, 3))
+        # Cast to object to avoid implicit cast when setting entry to pd.NaT below
+        df = DataFrame(np.random.randn(n, 3)).astype({0: object})
         df["dates1"] = date_range("1/1/2012", periods=n)
         df["dates3"] = date_range("1/1/2014", periods=n)
         df.iloc[0, 0] = pd.NaT
@@ -808,7 +809,8 @@ def test_date_index_query(self):
     def test_date_index_query_with_NaT(self):
         engine, parser = self.engine, self.parser
         n = 10
-        df = DataFrame(np.random.randn(n, 3))
+        # Cast to object to avoid implicit cast when setting entry to pd.NaT below
+        df = DataFrame(np.random.randn(n, 3)).astype({0: object})
         df["dates1"] = date_range("1/1/2012", periods=n)
         df["dates3"] = date_range("1/1/2014", periods=n)
         df.iloc[0, 0] = pd.NaT
diff --git a/pandas/tests/frame/test_reductions.py b/pandas/tests/frame/test_reductions.py
index a3cd3e4afdda1..2e0aa5fd0cf40 100644
--- a/pandas/tests/frame/test_reductions.py
+++ b/pandas/tests/frame/test_reductions.py
@@ -449,10 +449,14 @@ def test_var_std(self, datetime_frame):
     def test_numeric_only_flag(self, meth):
         # GH 9201
         df1 = DataFrame(np.random.randn(5, 3), columns=["foo", "bar", "baz"])
+        # Cast to object to avoid implicit cast when setting entry to "100" below
+        df1 = df1.astype({"foo": object})
         # set one entry to a number in str format
         df1.loc[0, "foo"] = "100"
 
         df2 = DataFrame(np.random.randn(5, 3), columns=["foo", "bar", "baz"])
+        # Cast to object to avoid implicit cast when setting entry to "a" below
+        df2 = df2.astype({"foo": object})
         # set one entry to a non-number str
         df2.loc[0, "foo"] = "a"
 
diff --git a/pandas/tests/groupby/test_timegrouper.py b/pandas/tests/groupby/test_timegrouper.py
index 4a707d8875db3..f16cf4dd27016 100644
--- a/pandas/tests/groupby/test_timegrouper.py
+++ b/pandas/tests/groupby/test_timegrouper.py
@@ -103,6 +103,8 @@ def test_groupby_with_timegrouper(self):
                     "20130901", "20131205", freq="5D", name="Date", inclusive="left"
                 ),
             )
+            # Cast to object to avoid implicit cast when setting entry to "CarlCarlCarl"
+            expected = expected.astype({"Buyer": object})
             expected.iloc[0, 0] = "CarlCarlCarl"
             expected.iloc[6, 0] = "CarlCarl"
             expected.iloc[18, 0] = "Joe"
diff --git a/pandas/tests/series/methods/test_replace.py b/pandas/tests/series/methods/test_replace.py
index 59afe22e40f7a..18ad275083022 100644
--- a/pandas/tests/series/methods/test_replace.py
+++ b/pandas/tests/series/methods/test_replace.py
@@ -16,7 +16,8 @@ def test_replace_explicit_none(self):
         expected = pd.Series([0, 0, None], dtype=object)
         tm.assert_series_equal(result, expected)
 
-        df = pd.DataFrame(np.zeros((3, 3)))
+        # Cast column 2 to object to avoid implicit cast when setting entry to ""
+        df = pd.DataFrame(np.zeros((3, 3))).astype({2: object})
         df.iloc[2, 2] = ""
         result = df.replace("", None)
         expected = pd.DataFrame(