diff --git a/CMakeLists.txt b/CMakeLists.txt
index ed06df5..f248572 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -140,6 +140,7 @@ add_executable(alltests
 	test/test_syslog_logger.cc
 	test/test_daemon.cc
 	test/test_change_user.cc
+	test/test_userdb.cc
 )
 
 target_include_directories(alltests PRIVATE
diff --git a/src/passwd/main.c b/src/passwd/main.c
index fda2171..f2313b4 100644
--- a/src/passwd/main.c
+++ b/src/passwd/main.c
@@ -173,7 +173,7 @@ static int add_user(struct args * args)
     }
 
     struct userdb * db = userdb_create(args->pepper);
-    userdb_load(db, args->file);
+    userdb_load_file(db, args->file);
     userdb_add(db, args->username, args->password);
     bool result = userdb_save(db, args->file);
     userdb_dispose(db);
@@ -191,7 +191,7 @@ static int remove_user(struct args * args)
     }
 
     struct userdb * db = userdb_create(args->pepper);
-    userdb_load(db, args->file);
+    userdb_load_file(db, args->file);
     userdb_remove(db, args->username);
     bool result = userdb_save(db, args->file);
     userdb_dispose(db);
@@ -216,7 +216,7 @@ static int check_password(struct args * args)
     }
 
     struct userdb * db = userdb_create(args->pepper);
-    userdb_load(db, args->file);
+    userdb_load_file(db, args->file);
     bool result = userdb_check(db, args->username, args->password);
     userdb_dispose(db);
 
diff --git a/src/userdb/userdb.c b/src/userdb/userdb.c
index 172742a..1eabdae 100644
--- a/src/userdb/userdb.c
+++ b/src/userdb/userdb.c
@@ -77,20 +77,17 @@ static char hex_char(unsigned char value)
 static char * to_hex(unsigned char const * value, size_t length)
 {
     char * result = malloc((2 * length) + 1);
-    if (NULL != result)
+    for (size_t i = 0, j = 0; i < length; i++, j+=2)
     {
-        for (size_t i = 0, j = 0; i < length; i++, j+=2)
-        {
-            unsigned char high = (value[i] >> 4) & 0x0f;
-            unsigned char low =   value[i]       & 0x0f;
+        unsigned char high = (value[i] >> 4) & 0x0f;
+        unsigned char low =   value[i]       & 0x0f;
 
-            result[j    ] = hex_char(high);
-            result[j + 1] = hex_char(low);
-        }
-
-        result[2 * length] = '\0';
+        result[j    ] = hex_char(high);
+        result[j + 1] = hex_char(low);
     }
 
+    result[2 * length] = '\0';
+
     return result;
 }
 
@@ -120,21 +117,46 @@ static char * compute_hash(
     }
 
     char * result = NULL;
+    EVP_MD_CTX * context = EVP_MD_CTX_new();        
+    EVP_DigestInit_ex(context, digest, NULL);        
+    EVP_DigestUpdate(context, password, strlen(password));
+    EVP_DigestUpdate(context, salt, strlen(salt));
+    EVP_DigestUpdate(context, db->pepper, strlen(db->pepper));
+
     unsigned int hash_size = EVP_MD_size(digest);
     unsigned char * hash = malloc(hash_size);
+    EVP_DigestFinal_ex(context, hash, &hash_size);
+    EVP_MD_CTX_free(context);
 
-    if (NULL != hash)
+    result = to_hex(hash, hash_size);
+    free(hash);
+
+    return result;
+}
+
+static bool userdb_load(
+    struct userdb * db,
+    json_t * container)
+{
+    bool result = false;
+    if (NULL != container)
     {
-        EVP_MD_CTX * context = EVP_MD_CTX_new();        
-        EVP_DigestInit_ex(context, digest, NULL);        
-        EVP_DigestUpdate(context, password, strlen(password));
-        EVP_DigestUpdate(context, salt, strlen(salt));
-        EVP_DigestUpdate(context, db->pepper, strlen(db->pepper));
-        EVP_DigestFinal_ex(context, hash, &hash_size);
-        EVP_MD_CTX_free(context);
+        json_t * meta = json_object_get(container, "meta");
+        json_t * users = json_object_get(container, "users");
 
-        result = to_hex(hash, hash_size);
-        free(hash);
+        if ((is_compatible(meta)) && (json_is_object(users))) {
+            json_t * hash_algorithm = json_object_get(meta, "hash_algorithm");
+            free(db->hash_algorithm);
+            db->hash_algorithm = strdup(json_string_value(hash_algorithm));
+
+            json_decref(db->users);
+            json_incref(users);
+            db->users = users;
+
+            result = true;
+        }
+
+        json_decref(container);
     }
 
     return result;
@@ -144,12 +166,9 @@ struct userdb * userdb_create(
     char const * pepper)
 {
     struct userdb * db = malloc(sizeof(struct userdb));
-    if (NULL != db)
-    {
-        db->users = json_object();
-        db->pepper = strdup(pepper);
-        db->hash_algorithm = strdup(USERDB_HASH_ALGORITHM);
-    }
+    db->users = json_object();
+    db->pepper = strdup(pepper);
+    db->hash_algorithm = strdup(USERDB_HASH_ALGORITHM);
 
     return db;
 }
@@ -184,36 +203,23 @@ bool userdb_save(
     return (0 == result);
 }
 
-
-bool userdb_load(
+bool userdb_load_file(
     struct userdb * db,
     char const * filename)
 {
-    bool result = false;
     json_t * container = json_load_file(filename, 0, NULL);
-    if (NULL != container)
-    {
-        json_t * meta = json_object_get(container, "meta");
-        json_t * users = json_object_get(container, "users");
-
-        if ((is_compatible(meta)) && (json_is_object(users))) {
-            json_t * hash_algorithm = json_object_get(meta, "hash_algorithm");
-            free(db->hash_algorithm);
-            db->hash_algorithm = strdup(json_string_value(hash_algorithm));
-
-            json_decref(db->users);
-            json_incref(users);
-            db->users = users;
-
-            result = true;
-        }
-
-        json_decref(container);
-    }
-
-    return result;
+    return userdb_load(db, container);
 }
 
+bool userdb_load_string(
+    struct userdb * db,
+    char const * contents)
+{
+    json_t * container = json_loads(contents, 0, NULL);
+    return userdb_load(db, container);
+}
+
+
 void userdb_add(
     struct userdb * db,
     char const * username,
@@ -243,7 +249,7 @@ static char const * json_object_get_string(
     json_t * object,
     char const * key)
 {
-    char const * result = NULL;
+    char const * result = "";
 
     json_t * string_holder = json_object_get(object, key);
     if (json_is_string(string_holder))
diff --git a/src/userdb/userdb.h b/src/userdb/userdb.h
index cf133d0..211051e 100644
--- a/src/userdb/userdb.h
+++ b/src/userdb/userdb.h
@@ -21,10 +21,14 @@ extern bool userdb_save(
     struct userdb * db,
     char const * filename);
 
-extern bool userdb_load(
+extern bool userdb_load_file(
     struct userdb * db,
     char const * filename);
 
+extern bool userdb_load_string(
+    struct userdb * db,
+    char const * contents);
+
 extern void userdb_add(
     struct userdb * db,
     char const * username,
diff --git a/src/webfused/auth/file_authenticator.c b/src/webfused/auth/file_authenticator.c
index 371bbeb..31737fc 100644
--- a/src/webfused/auth/file_authenticator.c
+++ b/src/webfused/auth/file_authenticator.c
@@ -37,7 +37,7 @@ wfd_file_authenticator_authenticate(
 	if ((NULL != username) && (NULL != password))
 	{
 		struct userdb * db = userdb_create("");
-		result = userdb_load(db, authenticator->filename); 
+		result = userdb_load_file(db, authenticator->filename); 
 		if (result)
 		{
 			result = userdb_check(db, username, password);
diff --git a/test/test_userdb.cc b/test/test_userdb.cc
new file mode 100644
index 0000000..7b4a1d4
--- /dev/null
+++ b/test/test_userdb.cc
@@ -0,0 +1,407 @@
+#include "userdb/userdb.h"
+#include <gtest/gtest.h>
+
+TEST(userdb, load_file)
+{
+    userdb * db = userdb_create("");
+
+    bool success = userdb_load_file(db, "test_passwd.json");
+    ASSERT_TRUE(success);
+
+    ASSERT_TRUE(userdb_check(db, "bob", "secret"));
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_file_failed_no_file)
+{
+    userdb * db = userdb_create("");
+
+    bool success = userdb_load_file(db, "non_existing.json");
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, save)
+{
+    {
+        userdb * db = userdb_create("");
+        userdb_add(db, "bob", "secret");
+        ASSERT_TRUE(userdb_save(db, "/tmp/webfused_test.json"));
+        userdb_dispose(db);
+    }
+
+    {
+        userdb * db = userdb_create("");
+        ASSERT_TRUE(userdb_load_file(db, "/tmp/webfused_test.json"));
+        ASSERT_TRUE(userdb_check(db, "bob", "secret"));
+        userdb_dispose(db);
+    }
+}
+
+
+TEST(userdb, add)
+{
+    userdb * db = userdb_create("");
+
+    userdb_add(db, "bob", "secret");
+    ASSERT_TRUE(userdb_check(db, "bob", "secret"));
+    ASSERT_FALSE(userdb_check(db, "bob", "i_dont_know"));
+    ASSERT_FALSE(userdb_check(db, "anna", "secret"));
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, remove)
+{
+    userdb * db = userdb_create("");
+    ASSERT_NE(nullptr, db);
+
+    userdb_add(db, "bob", "secret");
+    ASSERT_TRUE(userdb_check(db, "bob", "secret"));
+
+    userdb_remove(db, "bob");
+    ASSERT_FALSE(userdb_check(db, "bob", "secret"));
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, update)
+{
+    userdb * db = userdb_create("");
+    ASSERT_NE(nullptr, db);
+
+    userdb_add(db, "bob", "secret");
+    ASSERT_TRUE(userdb_check(db, "bob", "secret"));
+
+    userdb_add(db, "bob", "new_secret");
+    ASSERT_FALSE(userdb_check(db, "bob", "secret"));
+    ASSERT_TRUE(userdb_check(db, "bob", "new_secret"));
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_string)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"type\": \"wf-userdb\","
+        "    \"major\": 1,"
+        "    \"minor\": 0,"
+        "    \"hash_algorithm\": \"sha512\""
+        "},"
+        "\"users\": {"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_TRUE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_fail_no_json)
+{
+    userdb * db = userdb_create("");
+    char const contents[] = "brummni";
+
+    bool success = userdb_load_string(db, contents);
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_fail_invalid_type)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"type\": \"any-userdb\","
+        "    \"major\": 1,"
+        "    \"minor\": 0,"
+        "    \"hash_algorithm\": \"sha512\""
+        "},"
+        "\"users\": {"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_fail_invalid_version)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"type\": \"wf-userdb\","
+        "    \"major\": 2,"
+        "    \"minor\": 0,"
+        "    \"hash_algorithm\": \"sha512\""
+        "},"
+        "\"users\": {"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_fail_missing_type)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"major\": 1,"
+        "    \"minor\": 0,"
+        "    \"hash_algorithm\": \"sha512\""
+        "},"
+        "\"users\": {"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_fail_type_not_string)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"type\": 42,"
+        "    \"major\": 1,"
+        "    \"minor\": 0,"
+        "    \"hash_algorithm\": \"sha512\""
+        "},"
+        "\"users\": {"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_fail_missing_major_version)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"type\": \"wf-userdb\","
+        "    \"minor\": 0,"
+        "    \"hash_algorithm\": \"sha512\""
+        "},"
+        "\"users\": {"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_fail_major_version_not_int)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"type\": \"wf-userdb\","
+        "    \"major\": false,"
+        "    \"minor\": 0,"
+        "    \"hash_algorithm\": \"sha512\""
+        "},"
+        "\"users\": {"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_fail_missing_minor_version)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"type\": \"wf-userdb\","
+        "    \"major\": 1,"
+        "    \"hash_algorithm\": \"sha512\""
+        "},"
+        "\"users\": {"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_fail_minor_version_not_int)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"type\": \"wf-userdb\","
+        "    \"major\": 1,"
+        "    \"minor\": false,"
+        "    \"hash_algorithm\": \"sha512\""
+        "},"
+        "\"users\": {"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_fail_missing_hash_alg)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"type\": \"wf-userdb\","
+        "    \"major\": 1,"
+        "    \"minor\": 0,"
+        "},"
+        "\"users\": {"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_fail_hash_alg_not_string)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"type\": \"wf-userdb\","
+        "    \"major\": 1,"
+        "    \"minor\": 0,"
+        "    \"hash_algorithm\": 42"
+        "},"
+        "\"users\": {"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_fail_missing_meta)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"users\": {"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, load_fail_unsupported_hash)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"type\": \"wf-userdb\","
+        "    \"major\": 1,"
+        "    \"minor\": 0,"
+        "    \"hash_algorithm\": \"brummni\""
+        "},"
+        "\"users\": {"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_FALSE(success);
+
+    userdb_dispose(db);
+}
+
+TEST(userdb, fail_missing_user_salt)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"type\": \"wf-userdb\","
+        "    \"major\": 1,"
+        "    \"minor\": 0,"
+        "    \"hash_algorithm\": \"sha512\""
+        "},"
+        "\"users\": {"
+        "    \"bob\": {"
+        "      \"password_hash\": \"e51e27ce47054feead3d83068d47f2a07307d4877ac67da668ef43e0e466fe8c7b66651af14fdb8d48c51592ef5afa0c63f874d20861c6b9ef8e6513bfcaa330\""
+        "    }"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_TRUE(success);
+
+    ASSERT_FALSE(userdb_check(db, "bob", "secret"));
+    userdb_dispose(db);
+}
+
+TEST(userdb, fail_missing_user_hash)
+{
+    userdb * db = userdb_create("");
+    char const contents[] =
+        "{"
+        "\"meta\": {"
+        "    \"type\": \"wf-userdb\","
+        "    \"major\": 1,"
+        "    \"minor\": 0,"
+        "    \"hash_algorithm\": \"sha512\""
+        "},"
+        "\"users\": {"
+        "    \"bob\": {"
+        "      \"salt\": \"b3be6979921edecfea88c50d0d1ec40b7f8c383831b2276c65969ead18e47c03\""
+        "    }"
+        "}"
+        "}"
+        ;
+    bool success = userdb_load_string(db, contents);
+    ASSERT_TRUE(success);
+
+    ASSERT_FALSE(userdb_check(db, "bob", "secret"));
+    userdb_dispose(db);
+}
\ No newline at end of file