diff --git a/test/complexity_test.cc b/test/complexity_test.cc
new file mode 100644
index 0000000..323ddfe
--- /dev/null
+++ b/test/complexity_test.cc
@@ -0,0 +1,183 @@
+#undef NDEBUG
+#include <algorithm>
+#include <cassert>
+#include <cmath>
+#include <cstdlib>
+#include <vector>
+#include "benchmark/benchmark.h"
+#include "output_test.h"
+
+namespace {
+
+#define ADD_COMPLEXITY_CASES(...) \
+  int CONCAT(dummy, __LINE__) = AddComplexityTest(__VA_ARGS__)
+
+int AddComplexityTest(std::string test_name, std::string big_o_test_name,
+                      std::string rms_test_name, std::string big_o) {
+  SetSubstitutions({{"%name", test_name},
+                    {"%bigo_name", big_o_test_name},
+                    {"%rms_name", rms_test_name},
+                    {"%bigo_str", "[ ]* %float " + big_o},
+                    {"%bigo", big_o},
+                    {"%rms", "[ ]*[0-9]+ %"}});
+  AddCases(
+      TC_ConsoleOut,
+      {{"^%bigo_name %bigo_str %bigo_str[ ]*$"},
+       {"^%bigo_name", MR_Not},  // Assert we we didn't only matched a name.
+       {"^%rms_name %rms %rms[ ]*$", MR_Next}});
+  AddCases(TC_JSONOut, {{"\"name\": \"%bigo_name\",$"},
+                        {"\"run_name\": \"%name\",$", MR_Next},
+                        {"\"run_type\": \"aggregate\",$", MR_Next},
+                        {"\"aggregate_name\": \"BigO\",$", MR_Next},
+                        {"\"cpu_coefficient\": %float,$", MR_Next},
+                        {"\"real_coefficient\": %float,$", MR_Next},
+                        {"\"big_o\": \"%bigo\",$", MR_Next},
+                        {"\"time_unit\": \"ns\"$", MR_Next},
+                        {"}", MR_Next},
+                        {"\"name\": \"%rms_name\",$"},
+                        {"\"run_name\": \"%name\",$", MR_Next},
+                        {"\"run_type\": \"aggregate\",$", MR_Next},
+                        {"\"aggregate_name\": \"RMS\",$", MR_Next},
+                        {"\"rms\": %float$", MR_Next},
+                        {"}", MR_Next}});
+  AddCases(TC_CSVOut, {{"^\"%bigo_name\",,%float,%float,%bigo,,,,,$"},
+                       {"^\"%bigo_name\"", MR_Not},
+                       {"^\"%rms_name\",,%float,%float,,,,,,$", MR_Next}});
+  return 0;
+}
+
+}  // end namespace
+
+// ========================================================================= //
+// --------------------------- Testing BigO O(1) --------------------------- //
+// ========================================================================= //
+
+void BM_Complexity_O1(benchmark::State& state) {
+  for (auto _ : state) {
+    for (int i = 0; i < 1024; ++i) {
+      benchmark::DoNotOptimize(&i);
+    }
+  }
+  state.SetComplexityN(state.range(0));
+}
+BENCHMARK(BM_Complexity_O1)->Range(1, 1 << 18)->Complexity(benchmark::o1);
+BENCHMARK(BM_Complexity_O1)->Range(1, 1 << 18)->Complexity();
+BENCHMARK(BM_Complexity_O1)->Range(1, 1 << 18)->Complexity([](int64_t) {
+  return 1.0;
+});
+
+const char *one_test_name = "BM_Complexity_O1";
+const char *big_o_1_test_name = "BM_Complexity_O1_BigO";
+const char *rms_o_1_test_name = "BM_Complexity_O1_RMS";
+const char *enum_big_o_1 = "\\([0-9]+\\)";
+// FIXME: Tolerate both '(1)' and 'lgN' as output when the complexity is auto
+// deduced.
+// See https://github.com/google/benchmark/issues/272
+const char *auto_big_o_1 = "(\\([0-9]+\\))|(lgN)";
+const char *lambda_big_o_1 = "f\\(N\\)";
+
+// Add enum tests
+ADD_COMPLEXITY_CASES(one_test_name, big_o_1_test_name, rms_o_1_test_name,
+                     enum_big_o_1);
+
+// Add auto enum tests
+ADD_COMPLEXITY_CASES(one_test_name, big_o_1_test_name, rms_o_1_test_name,
+                     auto_big_o_1);
+
+// Add lambda tests
+ADD_COMPLEXITY_CASES(one_test_name, big_o_1_test_name, rms_o_1_test_name,
+                     lambda_big_o_1);
+
+// ========================================================================= //
+// --------------------------- Testing BigO O(N) --------------------------- //
+// ========================================================================= //
+
+std::vector<int> ConstructRandomVector(int64_t size) {
+  std::vector<int> v;
+  v.reserve(static_cast<int>(size));
+  for (int i = 0; i < size; ++i) {
+    v.push_back(static_cast<int>(std::rand() % size));
+  }
+  return v;
+}
+
+void BM_Complexity_O_N(benchmark::State& state) {
+  auto v = ConstructRandomVector(state.range(0));
+  // Test worst case scenario (item not in vector)
+  const int64_t item_not_in_vector = state.range(0) * 2;
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(std::find(v.begin(), v.end(), item_not_in_vector));
+  }
+  state.SetComplexityN(state.range(0));
+}
+BENCHMARK(BM_Complexity_O_N)
+    ->RangeMultiplier(2)
+    ->Range(1 << 10, 1 << 16)
+    ->Complexity(benchmark::oN);
+BENCHMARK(BM_Complexity_O_N)
+    ->RangeMultiplier(2)
+    ->Range(1 << 10, 1 << 16)
+    ->Complexity([](int64_t n) -> double { return static_cast<double>(n); });
+BENCHMARK(BM_Complexity_O_N)
+    ->RangeMultiplier(2)
+    ->Range(1 << 10, 1 << 16)
+    ->Complexity();
+
+const char *n_test_name = "BM_Complexity_O_N";
+const char *big_o_n_test_name = "BM_Complexity_O_N_BigO";
+const char *rms_o_n_test_name = "BM_Complexity_O_N_RMS";
+const char *enum_auto_big_o_n = "N";
+const char *lambda_big_o_n = "f\\(N\\)";
+
+// Add enum tests
+ADD_COMPLEXITY_CASES(n_test_name, big_o_n_test_name, rms_o_n_test_name,
+                     enum_auto_big_o_n);
+
+// Add lambda tests
+ADD_COMPLEXITY_CASES(n_test_name, big_o_n_test_name, rms_o_n_test_name,
+                     lambda_big_o_n);
+
+// ========================================================================= //
+// ------------------------- Testing BigO O(N*lgN) ------------------------- //
+// ========================================================================= //
+
+static void BM_Complexity_O_N_log_N(benchmark::State& state) {
+  auto v = ConstructRandomVector(state.range(0));
+  for (auto _ : state) {
+    std::sort(v.begin(), v.end());
+  }
+  state.SetComplexityN(state.range(0));
+}
+static const double kLog2E = 1.44269504088896340736;
+BENCHMARK(BM_Complexity_O_N_log_N)
+    ->RangeMultiplier(2)
+    ->Range(1 << 10, 1 << 16)
+    ->Complexity(benchmark::oNLogN);
+BENCHMARK(BM_Complexity_O_N_log_N)
+    ->RangeMultiplier(2)
+    ->Range(1 << 10, 1 << 16)
+    ->Complexity([](int64_t n) { return kLog2E * n * log(static_cast<double>(n)); });
+BENCHMARK(BM_Complexity_O_N_log_N)
+    ->RangeMultiplier(2)
+    ->Range(1 << 10, 1 << 16)
+    ->Complexity();
+
+const char *n_lg_n_test_name = "BM_Complexity_O_N_log_N";
+const char *big_o_n_lg_n_test_name = "BM_Complexity_O_N_log_N_BigO";
+const char *rms_o_n_lg_n_test_name = "BM_Complexity_O_N_log_N_RMS";
+const char *enum_auto_big_o_n_lg_n = "NlgN";
+const char *lambda_big_o_n_lg_n = "f\\(N\\)";
+
+// Add enum tests
+ADD_COMPLEXITY_CASES(n_lg_n_test_name, big_o_n_lg_n_test_name,
+                     rms_o_n_lg_n_test_name, enum_auto_big_o_n_lg_n);
+
+// Add lambda tests
+ADD_COMPLEXITY_CASES(n_lg_n_test_name, big_o_n_lg_n_test_name,
+                     rms_o_n_lg_n_test_name, lambda_big_o_n_lg_n);
+
+// ========================================================================= //
+// --------------------------- TEST CASES END ------------------------------ //
+// ========================================================================= //
+
+int main(int argc, char *argv[]) { RunOutputTests(argc, argv); }