diff --git a/src/certifi.erl b/src/certifi.erl
index 7be01a3..81f242d 100644
--- a/src/certifi.erl
+++ b/src/certifi.erl
@@ -6,6 +6,10 @@
 -export([cacertfile/0,
          cacerts/0]).
 
+-ifdef(TEST).
+-export([cacerts_test_data/0]).
+-endif.
+
 %% @doc CACertFile gives the path to the file with an X.509 certificate list
 %% containing the Mozilla CA Certificate that can then be used via the
 %% cacertfile setting in ssl options passed to the connect function.
@@ -29,4 +33,11 @@ cacertfile() ->
 %% passed to the connect function.
 -spec cacerts() -> [binary(),...].
 cacerts() ->
-    ok.
\ No newline at end of file
+    [].
+
+-ifdef(TEST).
+%% @doc CACertsTestData provides fixed certificates for testing.
+-spec cacerts_test_data() -> [binary(),...].
+cacerts_test_data() ->
+    [].
+-endif.
diff --git a/src/certifi_pt.erl b/src/certifi_pt.erl
index 3566ecf..f140023 100644
--- a/src/certifi_pt.erl
+++ b/src/certifi_pt.erl
@@ -1,27 +1,40 @@
 -module(certifi_pt).
 -export([parse_transform/2]).
 
+%% The function replace_cacerts/1 calls public_key:pem_decode/1.
+%% Dialyzer warns that public_key:pem_decode/1 is undefined because
+%% the public_key application is not listed in the certifi.app.src file.
+%% Since public_key is not required at runtime, we suppress this warning
+%% instead of adding public_key as a dependency.
+-dialyzer([{no_unknown, [replace_cacerts/1]}]).
+
 parse_transform(Forms, _Opts) ->
   [replace_cacerts(Form) || Form <- Forms].
 
-replace_cacerts({function, Ann, cacerts, 0, [_]}) ->
-  {ok, Binary} = file:read_file(cert_file() ),
+replace_cacerts({function, Ann, Function, 0, [_]}) when
+	Function =:= cacerts orelse Function =:= cacerts_test_data->
+  {ok, Binary} = file:read_file(cert_file(Function)),
   Pems = public_key:pem_decode(Binary),
   Cacerts = [Der || {'Certificate', Der, _} <- Pems],
   Body = lists:foldl(fun(Cert, Acc) ->
     {cons, 0, cert_to_bin_ast(Cert), Acc}
   end, {nil, 0}, Cacerts),
-  {function, Ann, cacerts, 0, [{clause, Ann, [], [], [Body]}]};
+  {function, Ann, Function, 0, [{clause, Ann, [], [], [Body]}]};
 replace_cacerts(Other) ->
   Other.
 
--spec cert_file() -> Result when
+-spec cert_file(Function) -> Result when
+	Function :: cacerts | cacerts_test_data,
 	Result :: file:filename_all().
-cert_file() ->
+cert_file(Function) ->
   AppDir = filename:dirname(
              filename:dirname(code:which(?MODULE))
             ),
-  filename:join([AppDir, "priv", "cacerts.pem"]).
+  Dir = case Function of
+    cacerts -> "priv";
+    cacerts_test_data -> "test/data"
+  end,
+  filename:join([AppDir, Dir, "cacerts.pem"]).
 
 -spec cert_to_bin_ast(Cert) -> Result when
 	Cert :: binary(),
diff --git a/test/certifi_tests.erl b/test/certifi_tests.erl
index 4ba2439..7218f5c 100644
--- a/test/certifi_tests.erl
+++ b/test/certifi_tests.erl
@@ -2,6 +2,9 @@
 
 -include_lib("eunit/include/eunit.hrl").
 
+%% Update this when updating priv/cacerts.pem.
+-define(NUM_OF_CERTS, 147).
+
 -ifdef('OTP_20_AND_ABOVE').
 reproducible_module_test() ->
     %% When compiled with +deterministic, only version is left out.
@@ -9,10 +12,17 @@ reproducible_module_test() ->
 -endif.
 
 cacerts_test_() ->
-    Certs = [Cert1, Cert2, Cert3 | _] = certifi:cacerts(),
-    [?_assertEqual(128, length(Certs))
-    ,?_assertMatch(<<48,130,5,192,48,130,3,168,160,3,2,1,2,2,16,30,191,89,80,184,_/binary>>, Cert1)
-    ,?_assertMatch(<<48,130,2,101,48,130,1,235,160,3,2,1,2,2,16,120,143,39,92,_/binary>>, Cert2)
-    ,?_assertMatch(<<48,130,5,239,48,130,3,215,160,3,2,1,2,2,8,13,211,227,188,_/binary>>, Cert3)
-    ,?_assertMatch(<<48,130,3,117,48,130,2,93,160,3,2,1,2,2,11,4,0,0,0,0,1,21,75,90,195,148,48,13,6,_/binary>>, lists:last(Certs))
+    %% Checking the contents is difficult because they change frequently.
+    %% Therefore, this test only checks the number and type of certificates.
+    Certs = certifi:cacerts(),
+    [?_assertEqual(?NUM_OF_CERTS, length(Certs))
+    ,?_assert(lists:all(fun is_binary/1, Certs))
+    ].
+
+cacerts_test_data_test_() ->
+    Certs = [Cert1, Cert2, Cert3] = certifi:cacerts_test_data(),
+    [?_assertEqual(3, length(Certs))
+    ,?_assertMatch(<<48,130,3,199,48,130,2,175,160,3,2,1,2,2,20,46,59,44,50,129,_/binary>>, Cert1)
+    ,?_assertMatch(<<48,130,3,199,48,130,2,175,160,3,2,1,2,2,20,22,71,8,124,36,_/binary>>, Cert2)
+    ,?_assertMatch(<<48,130,3,199,48,130,2,175,160,3,2,1,2,2,20,39,199,152,45,116,_/binary>>, Cert3)
     ].
diff --git a/test/data/cacerts.pem b/test/data/cacerts.pem
new file mode 100644
index 0000000..68c8784
--- /dev/null
+++ b/test/data/cacerts.pem
@@ -0,0 +1,71 @@
+-----BEGIN CERTIFICATE-----
+MIIDxzCCAq+gAwIBAgIUJ8eYLXRZClJruoSCfyQr/0phTOMwDQYJKoZIhvcNAQEL
+BQAwcjELMAkGA1UEBhMCWFgxDTALBgNVBAgMBEJFQU0xDzANBgNVBAcMBkVybGFu
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+eKGL33vz11++ozQ=
+-----END CERTIFICATE-----
+
+-----BEGIN CERTIFICATE-----
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+-----END CERTIFICATE-----
+
+-----BEGIN CERTIFICATE-----
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+-----END CERTIFICATE-----