tests(extgen): add integration tests (#1984)

Fix #1975

testdata/integration/basic_function.go

@@ -0,0 +1,32 @@
+package testintegration
+
+// #include <Zend/zend_types.h>
+import "C"
+import (
+	"strings"
+	"unsafe"
+
+	"github.com/dunglas/frankenphp"
+)
+
+// export_php:function test_uppercase(string $str): string
+func test_uppercase(s *C.zend_string) unsafe.Pointer {
+	str := frankenphp.GoString(unsafe.Pointer(s))
+	upper := strings.ToUpper(str)
+	return frankenphp.PHPString(upper, false)
+}
+
+// export_php:function test_add_numbers(int $a, int $b): int
+func test_add_numbers(a int64, b int64) int64 {
+	return a + b
+}
+
+// export_php:function test_multiply(float $a, float $b): float
+func test_multiply(a float64, b float64) float64 {
+	return a * b
+}
+
+// export_php:function test_is_enabled(bool $flag): bool
+func test_is_enabled(flag bool) bool {
+	return !flag
+}