PpdProvider v3: augment testing fake

This change implements
FakePrinterConfigCache::ConsumeFetchRequestFor(), which allows us to
write tests in which many things happen on-sequence before the server
has a chance to respond to an outstanding Fetch().

Bug: chromium:888189
Test: autoninja ... chrome{,os_unittests}
Change-Id: I747e43e3765ca2862a7274f9356ef95b76b99df6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2303042
Commit-Queue: Kalvin Lee <kdlee@chromium.org>
Reviewed-by: Sean Kau <skau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791389}

chromeos/printing/fake_printer_config_cache.cc

@@ -22,6 +22,15 @@ void FakePrinterConfigCache::SetFetchResponseForTesting(
     base::StringPiece key,
     base::StringPiece value) {
   contents_.insert_or_assign(std::string(key), std::string(value));
+
+  // If Fetch(|key|) was previously being consumed by prior call to
+  // DiscardFetchRequestFor(), we unblock it now.
+  fetch_requests_to_ignore_.erase(key);
+}
+
+void FakePrinterConfigCache::DiscardFetchRequestFor(base::StringPiece key) {
+  fetch_requests_to_ignore_.insert(std::string(key));
+  contents_.erase(key);
 }
 
 void FakePrinterConfigCache::Fetch(const std::string& key,
@@ -31,12 +40,20 @@ void FakePrinterConfigCache::Fetch(const std::string& key,
     std::move(cb).Run(PrinterConfigCache::FetchResult::Success(
         key, contents_.at(key), base::Time()));
     return;
+  } else if (fetch_requests_to_ignore_.contains(key)) {
+    // Caller has directed us, by way of DiscardFetchRequestFor(), to
+    // _not_ respond to this Fetch().
+    return;
   }
   std::move(cb).Run(PrinterConfigCache::FetchResult::Failure(key));
 }
 
 void FakePrinterConfigCache::Drop(const std::string& key) {
   contents_.erase(key);
+
+  // If Fetch(|key|) was previously being consumed by prior call to
+  // DiscardFetchRequestFor(), we unblock it now.
+  fetch_requests_to_ignore_.erase(key);
 }
 
 }  // namespace chromeos

chromeos/printing/fake_printer_config_cache.h

@@ -8,6 +8,7 @@
 #include <string>
 
 #include "base/containers/flat_map.h"
+#include "base/containers/flat_set.h"
 #include "base/strings/string_piece.h"
 #include "base/time/clock.h"
 #include "chromeos/printing/printer_config_cache.h"
@@ -40,8 +41,19 @@ class CHROMEOS_EXPORT FakePrinterConfigCache : public PrinterConfigCache {
   void SetFetchResponseForTesting(base::StringPiece key,
                                   base::StringPiece value);
 
+  // Sets internal state of |this| s.t. future Fetch() calls for
+  // |key| are consumed (i.e. delayed indefinitely and never called
+  // back). The effects of this are undone by a subsequent call to
+  // SetFetchResponseForTesting() or to Drop().
+  //
+  // This method is useful for simulating a slow server: one that
+  // doesn't immediately respond to a Fetch() request (in fact, it
+  // never responds at all, so use this carefully).
+  void DiscardFetchRequestFor(base::StringPiece key);
+
  private:
   base::flat_map<std::string, std::string> contents_;
+  base::flat_set<std::string> fetch_requests_to_ignore_;
 };
 
 }  // namespace chromeos