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tests: internal: add unit tests for log_sampling processor
Add unit tests for sampling algorithms: - Fixed window sampling and window resets - Sliding window with bucket expiration - Exponential decay rate calculations - Edge cases and boundary conditions Signed-off-by: Jorge Niedbalski <[email protected]>
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‎tests/internal/CMakeLists.txt

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@@ -153,6 +153,13 @@ if(FLB_LUAJIT)
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)
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endif()
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if(FLB_PROCESSOR_LOG_SAMPLING)
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set(UNIT_TESTS_FILES
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${UNIT_TESTS_FILES}
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log_sampling.c
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)
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endif()
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set(UNIT_TESTS_DATA
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data/tls/certificate.pem
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data/tls/private_key.pem

‎tests/internal/log_sampling.c

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/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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/* Fluent Bit
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* ==========
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* Copyright (C) 2015-2025 The Fluent Bit Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <fluent-bit/flb_info.h>
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#include <fluent-bit/flb_mem.h>
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#include <fluent-bit/flb_time.h>
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#include "flb_tests_internal.h"
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/* Import the sampling functions from the processor plugin */
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#include "../../plugins/processor_log_sampling/log_sampling.h"
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static void test_fixed_window_basic()
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{
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struct sampling_state state = {0};
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int result;
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int i;
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int sampled_count = 0;
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time_t current_time = 1000; /* Start time */
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int window_size = 60;
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int max_logs = 5;
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/* Initialize state */
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state.window_start = current_time;
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state.current_window_count = 0;
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/* Test: First 5 logs should be sampled */
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for (i = 0; i < 10; i++) {
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result = flb_sampling_fixed_window(&state, current_time, window_size, max_logs);
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if (result == FLB_TRUE) {
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sampled_count++;
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}
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}
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TEST_CHECK(sampled_count == 5);
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TEST_MSG("Fixed window: sampled %d out of 10 (expected 5)", sampled_count);
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/* Test: New window should reset the count */
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current_time += window_size + 1; /* Move to next window */
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sampled_count = 0;
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for (i = 0; i < 3; i++) {
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result = flb_sampling_fixed_window(&state, current_time, window_size, max_logs);
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if (result == FLB_TRUE) {
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sampled_count++;
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}
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}
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TEST_CHECK(sampled_count == 3);
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TEST_MSG("Fixed window (new): sampled %d out of 3 (expected 3)", sampled_count);
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}
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static void test_sliding_window_basic()
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{
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struct sampling_state state = {0};
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int result;
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int i;
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int sampled_count = 0;
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time_t current_time = 1000;
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int window_size = 10;
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int max_logs = 5;
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/* Initialize sliding window buckets */
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state.bucket_count = window_size;
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state.buckets = flb_calloc(state.bucket_count, sizeof(*state.buckets));
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TEST_CHECK(state.buckets != NULL);
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/* Test: First 5 logs should be sampled */
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for (i = 0; i < 7; i++) {
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result = flb_sampling_sliding_window(&state, current_time, window_size, max_logs);
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if (result == FLB_TRUE) {
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sampled_count++;
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}
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/* Advance time slightly to distribute across buckets */
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if (i % 2 == 0) {
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current_time++;
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}
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}
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TEST_CHECK(sampled_count == 5);
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TEST_MSG("Sliding window: sampled %d out of 7 (expected 5)", sampled_count);
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/* Test: Old entries should expire */
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current_time += window_size + 2; /* Move past window */
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sampled_count = 0;
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for (i = 0; i < 3; i++) {
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result = flb_sampling_sliding_window(&state, current_time, window_size, max_logs);
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if (result == FLB_TRUE) {
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sampled_count++;
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}
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}
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TEST_CHECK(sampled_count == 3);
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TEST_MSG("Sliding window (after expiry): sampled %d out of 3 (expected 3)", sampled_count);
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flb_free(state.buckets);
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}
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static void test_exponential_decay_basic()
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{
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int result;
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int i;
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int sampled_count;
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time_t window_start = 1000;
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time_t current_time = 1000;
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double base_rate = 1.0; /* 100% initially */
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double decay_factor = 0.5; /* 50% reduction per interval */
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int decay_interval = 10;
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/* Seed random for reproducible tests */
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srand(12345);
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/* Test: First interval should sample most logs (rate=1.0) */
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sampled_count = 0;
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for (i = 0; i < 100; i++) {
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result = flb_sampling_exponential(window_start, current_time,
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base_rate, decay_factor, decay_interval);
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if (result == FLB_TRUE) {
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sampled_count++;
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}
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}
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/* With rate=1.0, should sample all or nearly all */
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TEST_CHECK(sampled_count >= 95);
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TEST_MSG("Exponential (interval 0): sampled %d out of 100 (expected >= 95)", sampled_count);
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/* Test: Second interval should sample about 50% */
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current_time = window_start + decay_interval;
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sampled_count = 0;
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for (i = 0; i < 100; i++) {
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result = flb_sampling_exponential(window_start, current_time,
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base_rate, decay_factor, decay_interval);
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if (result == FLB_TRUE) {
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sampled_count++;
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}
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}
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/* With rate=0.5, should sample roughly 40-60% */
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TEST_CHECK(sampled_count >= 40 && sampled_count <= 60);
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TEST_MSG("Exponential (interval 1): sampled %d out of 100 (expected 40-60)", sampled_count);
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/* Test: Third interval should sample about 25% */
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current_time = window_start + (2 * decay_interval);
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sampled_count = 0;
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for (i = 0; i < 100; i++) {
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result = flb_sampling_exponential(window_start, current_time,
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base_rate, decay_factor, decay_interval);
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if (result == FLB_TRUE) {
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sampled_count++;
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}
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}
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/* With rate=0.25, should sample roughly 20-30% */
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TEST_CHECK(sampled_count >= 15 && sampled_count <= 35);
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TEST_MSG("Exponential (interval 2): sampled %d out of 100 (expected 15-35)", sampled_count);
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}
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static void test_fixed_window_edge_cases()
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{
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struct sampling_state state = {0};
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int result;
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time_t current_time = 1000;
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int window_size = 60;
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int max_logs = 0; /* Edge case: no logs allowed */
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/* Test: max_logs = 0 should reject all */
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state.window_start = current_time;
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state.current_window_count = 0;
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result = flb_sampling_fixed_window(&state, current_time, window_size, max_logs);
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TEST_CHECK(result == FLB_FALSE);
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/* Test: Window boundary */
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max_logs = 1;
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state.current_window_count = 0;
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result = flb_sampling_fixed_window(&state, current_time, window_size, max_logs);
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TEST_CHECK(result == FLB_TRUE);
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/* Move to exact window boundary */
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current_time = state.window_start + window_size;
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result = flb_sampling_fixed_window(&state, current_time, window_size, max_logs);
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TEST_CHECK(result == FLB_TRUE); /* New window should allow */
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TEST_CHECK(state.current_window_count == 1);
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}
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static void test_sliding_window_edge_cases()
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{
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struct sampling_state state = {0};
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int result;
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time_t current_time = 1000;
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int window_size = 1; /* Minimal window */
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int max_logs = 1;
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/* Initialize with minimal bucket */
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state.bucket_count = 1;
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state.buckets = flb_calloc(1, sizeof(*state.buckets));
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TEST_CHECK(state.buckets != NULL);
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/* Test: Single bucket behavior */
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result = flb_sampling_sliding_window(&state, current_time, window_size, max_logs);
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TEST_CHECK(result == FLB_TRUE);
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result = flb_sampling_sliding_window(&state, current_time, window_size, max_logs);
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TEST_CHECK(result == FLB_FALSE); /* Already at limit */
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/* Test: Bucket expiry */
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current_time += window_size + 1;
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result = flb_sampling_sliding_window(&state, current_time, window_size, max_logs);
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TEST_CHECK(result == FLB_TRUE); /* Old bucket should be expired */
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flb_free(state.buckets);
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}
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TEST_LIST = {
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{ "fixed_window_basic", test_fixed_window_basic },
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{ "sliding_window_basic", test_sliding_window_basic },
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{ "exponential_decay_basic", test_exponential_decay_basic },
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{ "fixed_window_edge_cases", test_fixed_window_edge_cases },
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{ "sliding_window_edge_cases", test_sliding_window_edge_cases },
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{ 0 }
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};

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