Reduce the number of QUIC end-to-end test combinations that are from from 240 to 46, by looking at …

net/tools/quic/end_to_end_test.cc

Index: net/tools/quic/end_to_end_test.cc
diff --git a/net/tools/quic/end_to_end_test.cc b/net/tools/quic/end_to_end_test.cc
index 5907cd08ccd35e84992a58dedad812585e90fa39..c6a0a91d7199b7336fe034d57d923bacb31cc642 100644
--- a/net/tools/quic/end_to_end_test.cc
+++ b/net/tools/quic/end_to_end_test.cc
@@ -147,30 +147,51 @@ vector<TestParams> GetTestParams() {
   // to do 0-RTT across incompatible versions. Chromium only supports
   // a single version at a time anyway. :)
   QuicVersionVector all_supported_versions = QuicSupportedVersions();
-  QuicVersionVector client_version_buckets[2];
+  QuicVersionVector version_buckets[2];
   for (const QuicVersion version : all_supported_versions) {
     if (version <= QUIC_VERSION_25) {
       // SPDY/4
-      client_version_buckets[0].push_back(version);
+      version_buckets[0].push_back(version);
     } else {
       // QUIC_VERSION_26 changes the kdf in a way that is incompatible with
       // version negotiation across the version 26 boundary.
-      client_version_buckets[1].push_back(version);
+      version_buckets[1].push_back(version);
     }
   }
 
   vector<TestParams> params;
-  // TODO(rtenneti): Add kTBBR after BBR code is checked in.
-  // for (const QuicTag congestion_control_tag : {kRENO, kTBBR, kQBIC}) {
-  for (const QuicTag congestion_control_tag : {kRENO, kQBIC}) {
-    for (const bool use_fec : {false, true}) {
-      for (const QuicVersionVector& client_versions : client_version_buckets) {
-        // A number of end to end tests fail when stateless rejects are enabled
-        // *and* there are more than two QUIC versions.
-        for (bool client_supports_stateless_rejects : {true, false}) {
-          for (bool server_uses_stateless_rejects_if_peer_supported :
-               {true, false}) {
-            for (bool auto_tune_flow_control_window : {true, false}) {
+  for (bool server_uses_stateless_rejects_if_peer_supported : {true, false}) {
+    for (bool client_supports_stateless_rejects : {true, false}) {
+      // TODO(rtenneti): Add kTBBR after BBR code is checked in.
+      for (const QuicTag congestion_control_tag : {kRENO, kQBIC}) {
+        for (bool auto_tune_flow_control_window : {true, false}) {
+          for (const bool use_fec : {false, true}) {
+            const int kMaxEnabledOptions = 5;
+            int enabled_options = 0;
+            if (congestion_control_tag != kQBIC) {
+              ++enabled_options;
+            }
+            if (use_fec) {
+              ++enabled_options;
+            }
+            if (auto_tune_flow_control_window) {
+              ++enabled_options;
+            }
+            if (client_supports_stateless_rejects) {
+              ++enabled_options;
+            }
+            if (server_uses_stateless_rejects_if_peer_supported) {
+              ++enabled_options;
+            }
+            CHECK_GE(kMaxEnabledOptions, enabled_options);
+
+            // Run tests with no options, a single option, or all the options
+            // enabled to avoid a combinatorial explosion.
+            if (enabled_options > 1 && enabled_options < kMaxEnabledOptions) {
+              continue;
+            }
+
+            for (const QuicVersionVector& client_versions : version_buckets) {
               CHECK(!client_versions.empty());
               // Add an entry for server and client supporting all versions.
               params.push_back(TestParams(