Add unit test for Database::createFunction()

using an example from
https://stackoverflow.com/a/8283265/1163698 How can I create a user-defined function in SQLite?

Author: SRombauts

include/SQLiteCpp/Database.h

@@ -336,9 +336,9 @@ class Database
                         bool        abDeterministic,
                         void*       apApp,
                         void      (*apFunc)(sqlite3_context *, int, sqlite3_value **),
-                        void      (*apStep)(sqlite3_context *, int, sqlite3_value **),
-                        void      (*apFinal)(sqlite3_context *),  // NOLINT(readability/casting)
-                        void      (*apDestroy)(void *));
+                        void      (*apStep)(sqlite3_context *, int, sqlite3_value **) = nullptr,
+                        void      (*apFinal)(sqlite3_context *) = nullptr,  // NOLINT(readability/casting)
+                        void      (*apDestroy)(void *) = nullptr);
 
     /**
      * @brief Create or redefine a SQL function or aggregate in the sqlite database.
@@ -364,12 +364,12 @@ class Database
                                bool                 abDeterministic,
                                void*                apApp,
                                void               (*apFunc)(sqlite3_context *, int, sqlite3_value **),
-                               void               (*apStep)(sqlite3_context *, int, sqlite3_value **),
-                               void               (*apFinal)(sqlite3_context *), // NOLINT(readability/casting)
-                               void               (*apDestroy)(void *))
+                               void               (*apStep)(sqlite3_context *, int, sqlite3_value **) = nullptr,
+                               void               (*apFinal)(sqlite3_context *) = nullptr,
+                               void               (*apDestroy)(void *) = nullptr)
     {
-        return createFunction(aFuncName.c_str(), aNbArg, abDeterministic,
-                              apApp, apFunc, apStep, apFinal, apDestroy);
+        createFunction(aFuncName.c_str(), aNbArg, abDeterministic,
+                       apApp, apFunc, apStep, apFinal, apDestroy);
     }
 
     /**

src/Database.cpp

@@ -192,17 +192,17 @@ void Database::createFunction(const char*   apFuncName,
                               bool          abDeterministic,
                               void*         apApp,
                               void        (*apFunc)(sqlite3_context *, int, sqlite3_value **),
-                              void        (*apStep)(sqlite3_context *, int, sqlite3_value **),
-                              void        (*apFinal)(sqlite3_context *),   // NOLINT(readability/casting)
-                              void        (*apDestroy)(void *))
+                              void        (*apStep)(sqlite3_context *, int, sqlite3_value **) /* = nullptr */,
+                              void        (*apFinal)(sqlite3_context *) /* = nullptr */, // NOLINT(readability/casting)
+                              void        (*apDestroy)(void *) /* = nullptr */)
 {
-    int TextRep = SQLITE_UTF8;
+    int textRep = SQLITE_UTF8;
     // optimization if deterministic function (e.g. of nondeterministic function random())
     if (abDeterministic)
     {
-        TextRep = TextRep|SQLITE_DETERMINISTIC;
+        textRep = textRep | SQLITE_DETERMINISTIC;
     }
-    const int ret = sqlite3_create_function_v2(mpSQLite, apFuncName, aNbArg, TextRep,
+    const int ret = sqlite3_create_function_v2(mpSQLite, apFuncName, aNbArg, textRep,
                                                apApp, apFunc, apStep, apFinal, apDestroy);
     check(ret);
 }

tests/Database_test.cpp

@@ -311,7 +311,40 @@ TEST(Database, execException)
     EXPECT_STREQ("table test has 3 columns but 4 values were supplied", db.getErrorMsg());
 }
 
-// TODO: test Database::createFunction()
+// From https://stackoverflow.com/a/8283265/1163698 How can I create a user-defined function in SQLite?
+static void firstchar(sqlite3_context *context, int argc, sqlite3_value **argv)
+{
+    if (argc == 1)
+    {
+        const unsigned char *text = sqlite3_value_text(argv[0]);
+        if (text && text[0])
+        {
+            char result[2];
+            result[0] = text[0]; result[1] = '\0';
+            sqlite3_result_text(context, result, -1, SQLITE_TRANSIENT);
+            return;
+        }
+    }
+    sqlite3_result_null(context);
+}
+
+TEST(Database, createFunction)
+{
+    // Create a new database
+    SQLite::Database db(":memory:", SQLite::OPEN_READWRITE);
+    db.exec("CREATE TABLE test (id INTEGER PRIMARY KEY, value TEXT)");
+
+    EXPECT_EQ(1, db.exec("INSERT INTO test VALUES (NULL, \"first\")"));
+    EXPECT_EQ(1, db.exec("INSERT INTO test VALUES (NULL, \"second\")"));
+
+    // exception with SQL error: "no such function: firstchar"
+    EXPECT_THROW(db.exec("SELECT firstchar(value) FROM test WHERE id=1"), SQLite::Exception);
+
+    db.createFunction("firstchar", 1, true, nullptr, &firstchar, nullptr, nullptr, nullptr);
+    
+    EXPECT_EQ(1, db.exec("SELECT firstchar(value) FROM test WHERE id=1"));
+}
+
 // TODO: test Database::loadExtension()
 
 #ifdef SQLITE_HAS_CODEC