Do more page load/unload checks in EmbedderTest.

- Keep track of pages in a single map when calling LoadPage(). It is
  simpler and performance is not crucial as the number of loaded pages
  is usually very small.
- Verify UnloadPage() is only called for loaded pages.
- Verify there are no loaded pages in TearDown().
- Verify RenderLoadedPage methods are only rendering loaded pages.
- Fix pages that are using FPDF_LoadPage() and FPDF_ClosePage() when
  they should be using LoadPage() and UnloadPage().
- Disallow calling LoadPage() for the same page number repeatedly. No
  caller does this and it makes verification in UnloadPage() harder.

Change-Id: I58878ea8ade21dde28f1bbebd3a3304ce677561d
Reviewed-on: https://pdfium-review.googlesource.com/25550
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>

7 files changed, 89 insertions, 51 deletions

diff --git a/fpdfsdk/fpdf_structtree_embeddertest.cpp b/fpdfsdk/fpdf_structtree_embeddertest.cpp
index 7ca81f7b2e..b638cdc315 100644
--- a/fpdfsdk/fpdf_structtree_embeddertest.cpp
+++ b/fpdfsdk/fpdf_structtree_embeddertest.cpp
@@ -71,7 +71,7 @@ TEST_F(FPDFStructTreeEmbeddertest, GetAltText) {
   EXPECT_EQ(nullptr, ggchild_element);
 
   FPDF_StructTree_Close(struct_tree);
-  FPDF_ClosePage(page);
+  UnloadPage(page);
 }
 
 TEST_F(FPDFStructTreeEmbeddertest, GetMarkedContentID) {
@@ -87,7 +87,7 @@ TEST_F(FPDFStructTreeEmbeddertest, GetMarkedContentID) {
   EXPECT_EQ(0, FPDF_StructElement_GetMarkedContentID(element));
 
   FPDF_StructTree_Close(struct_tree);
-  FPDF_ClosePage(page);
+  UnloadPage(page);
 }
 
 TEST_F(FPDFStructTreeEmbeddertest, GetType) {
@@ -116,5 +116,5 @@ TEST_F(FPDFStructTreeEmbeddertest, GetType) {
             WideString::FromUTF16LE(buffer, FXSYS_len(kExpected)));
 
   FPDF_StructTree_Close(struct_tree);
-  FPDF_ClosePage(page);
+  UnloadPage(page);
 }
diff --git a/fpdfsdk/fpdfannot_embeddertest.cpp b/fpdfsdk/fpdfannot_embeddertest.cpp
index 5b5c29717b..5406397375 100644
--- a/fpdfsdk/fpdfannot_embeddertest.cpp
+++ b/fpdfsdk/fpdfannot_embeddertest.cpp
@@ -31,7 +31,7 @@ std::string BufferToString(const std::vector<char>& buf) {
 TEST_F(FPDFAnnotEmbeddertest, RenderAnnotWithOnlyRolloverAP) {
   // Open a file with one annotation and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_highlight_rollover_ap.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
 
   // This annotation has a malformed appearance stream, which does not have its
@@ -48,6 +48,9 @@ TEST_F(FPDFAnnotEmbeddertest, RenderAnnotWithOnlyRolloverAP) {
 TEST_F(FPDFAnnotEmbeddertest, ExtractHighlightLongContent) {
   // Open a file with one annotation and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_highlight_long_content.pdf"));
+  // TODO(thestig): This test should use LoadPage() and UnloadPage(), but one of
+  // the FORM API calls in LoadPage() makes this test fail. So use
+  // FPDF_LoadPage() and FPDF_ClosePage() for now.
   FPDF_PAGE page = FPDF_LoadPage(document(), 0);
   ASSERT_TRUE(page);
 
@@ -66,7 +69,7 @@ TEST_F(FPDFAnnotEmbeddertest, ExtractHighlightLongContent) {
     unsigned int G;
     unsigned int B;
     unsigned int A;
-    EXPECT_TRUE(FPDFAnnot_GetColor(annot.get(), FPDFANNOT_COLORTYPE_Color, &R,
+    ASSERT_TRUE(FPDFAnnot_GetColor(annot.get(), FPDFANNOT_COLORTYPE_Color, &R,
                                    &G, &B, &A));
     EXPECT_EQ(255u, R);
     EXPECT_EQ(255u, G);
@@ -123,12 +126,15 @@ TEST_F(FPDFAnnotEmbeddertest, ExtractHighlightLongContent) {
     EXPECT_EQ(157.211182f, quadpoints.x4);
     EXPECT_EQ(706.264465f, quadpoints.y4);
   }
-  UnloadPage(page);
+  FPDF_ClosePage(page);
 }
 
 TEST_F(FPDFAnnotEmbeddertest, ExtractInkMultiple) {
   // Open a file with three annotations and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_ink_multiple.pdf"));
+  // TODO(thestig): This test should use LoadPage() and UnloadPage(), but one of
+  // the FORM API calls in LoadPage() makes this test fail. So use
+  // FPDF_LoadPage() and FPDF_ClosePage() for now.
   FPDF_PAGE page = FPDF_LoadPage(document(), 0);
   ASSERT_TRUE(page);
 
@@ -147,7 +153,7 @@ TEST_F(FPDFAnnotEmbeddertest, ExtractInkMultiple) {
     unsigned int G;
     unsigned int B;
     unsigned int A;
-    EXPECT_TRUE(FPDFAnnot_GetColor(annot.get(), FPDFANNOT_COLORTYPE_Color, &R,
+    ASSERT_TRUE(FPDFAnnot_GetColor(annot.get(), FPDFANNOT_COLORTYPE_Color, &R,
                                    &G, &B, &A));
     EXPECT_EQ(0u, R);
     EXPECT_EQ(0u, G);
@@ -167,13 +173,13 @@ TEST_F(FPDFAnnotEmbeddertest, ExtractInkMultiple) {
     EXPECT_EQ(475.336090f, rect.right);
     EXPECT_EQ(681.535034f, rect.top);
   }
-  UnloadPage(page);
+  FPDF_ClosePage(page);
 }
 
 TEST_F(FPDFAnnotEmbeddertest, AddIllegalSubtypeAnnotation) {
   // Open a file with one annotation and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_highlight_long_content.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
 
   // Add an annotation with an illegal subtype.
@@ -185,7 +191,7 @@ TEST_F(FPDFAnnotEmbeddertest, AddIllegalSubtypeAnnotation) {
 TEST_F(FPDFAnnotEmbeddertest, AddFirstTextAnnotation) {
   // Open a file with no annotation and load its first page.
   ASSERT_TRUE(OpenDocument("hello_world.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
   EXPECT_EQ(0, FPDFPage_GetAnnotCount(page));
 
@@ -216,7 +222,7 @@ TEST_F(FPDFAnnotEmbeddertest, AddFirstTextAnnotation) {
     unsigned int G;
     unsigned int B;
     unsigned int A;
-    EXPECT_TRUE(FPDFAnnot_GetColor(annot.get(), FPDFANNOT_COLORTYPE_Color, &R,
+    ASSERT_TRUE(FPDFAnnot_GetColor(annot.get(), FPDFANNOT_COLORTYPE_Color, &R,
                                    &G, &B, &A));
     EXPECT_EQ(51u, R);
     EXPECT_EQ(102u, G);
@@ -227,7 +233,7 @@ TEST_F(FPDFAnnotEmbeddertest, AddFirstTextAnnotation) {
     ASSERT_TRUE(FPDFAnnot_SetColor(annot.get(), FPDFANNOT_COLORTYPE_Color, 204,
                                    153, 102, 51));
     // Check that the color has been set correctly.
-    EXPECT_TRUE(FPDFAnnot_GetColor(annot.get(), FPDFANNOT_COLORTYPE_Color, &R,
+    ASSERT_TRUE(FPDFAnnot_GetColor(annot.get(), FPDFANNOT_COLORTYPE_Color, &R,
                                    &G, &B, &A));
     EXPECT_EQ(204u, R);
     EXPECT_EQ(153u, G);
@@ -272,7 +278,7 @@ TEST_F(FPDFAnnotEmbeddertest, AddFirstTextAnnotation) {
 TEST_F(FPDFAnnotEmbeddertest, AddAndSaveUnderlineAnnotation) {
   // Open a file with one annotation and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_highlight_long_content.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
 
   // Check that there is a total of one annotation on its first page, and verify
@@ -302,7 +308,7 @@ TEST_F(FPDFAnnotEmbeddertest, AddAndSaveUnderlineAnnotation) {
 
   // Save the document, closing the page and document.
   EXPECT_TRUE(FPDF_SaveAsCopy(document(), this, 0));
-  FPDF_ClosePage(page);
+  UnloadPage(page);
 
   // Open the saved document.
   const char md5[] = "dba153419f67b7c0c0e3d22d3e8910d5";
@@ -351,7 +357,7 @@ TEST_F(FPDFAnnotEmbeddertest, ModifyRectQuadpointsWithAP) {
 
   // Open a file with four annotations and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_highlight_square_with_ap.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
   EXPECT_EQ(4, FPDFPage_GetAnnotCount(page));
 
@@ -449,6 +455,9 @@ TEST_F(FPDFAnnotEmbeddertest, ModifyRectQuadpointsWithAP) {
 TEST_F(FPDFAnnotEmbeddertest, RemoveAnnotation) {
   // Open a file with 3 annotations on its first page.
   ASSERT_TRUE(OpenDocument("annotation_ink_multiple.pdf"));
+  // TODO(thestig): This test should use LoadPage() and UnloadPage(), but one of
+  // the FORM API calls in LoadPage() makes this test fail. So use
+  // FPDF_LoadPage() and FPDF_ClosePage() for now.
   FPDF_PAGE page = FPDF_LoadPage(document(), 0);
   ASSERT_TRUE(page);
   EXPECT_EQ(3, FPDFPage_GetAnnotCount(page));
@@ -542,7 +551,7 @@ TEST_F(FPDFAnnotEmbeddertest, AddAndModifyPath) {
 
   // Open a file with two annotations and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_stamp_with_ap.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
   EXPECT_EQ(2, FPDFPage_GetAnnotCount(page));
 
@@ -635,7 +644,7 @@ TEST_F(FPDFAnnotEmbeddertest, AddAndModifyPath) {
 
   // Save the document, closing the page and document.
   EXPECT_TRUE(FPDF_SaveAsCopy(document(), this, 0));
-  FPDF_ClosePage(page);
+  UnloadPage(page);
 
   // Open the saved document.
   OpenSavedDocument();
@@ -667,7 +676,7 @@ TEST_F(FPDFAnnotEmbeddertest, AddAndModifyPath) {
 TEST_F(FPDFAnnotEmbeddertest, ModifyAnnotationFlags) {
   // Open a file with an annotation and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_highlight_rollover_ap.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
 
   // Check that the page renders correctly.
@@ -730,7 +739,7 @@ TEST_F(FPDFAnnotEmbeddertest, AddAndModifyImage) {
 
   // Open a file with two annotations and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_stamp_with_ap.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
   EXPECT_EQ(2, FPDFPage_GetAnnotCount(page));
 
@@ -792,7 +801,7 @@ TEST_F(FPDFAnnotEmbeddertest, AddAndModifyImage) {
 
   // Save the document, closing the page and document.
   EXPECT_TRUE(FPDF_SaveAsCopy(document(), this, 0));
-  FPDF_ClosePage(page);
+  UnloadPage(page);
   FPDFBitmap_Destroy(image_bitmap);
 
   // Test that the saved document renders the modified image object correctly.
@@ -812,7 +821,7 @@ TEST_F(FPDFAnnotEmbeddertest, AddAndModifyText) {
 
   // Open a file with two annotations and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_stamp_with_ap.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
   EXPECT_EQ(2, FPDFPage_GetAnnotCount(page));
 
@@ -884,7 +893,7 @@ TEST_F(FPDFAnnotEmbeddertest, AddAndModifyText) {
 TEST_F(FPDFAnnotEmbeddertest, GetSetStringValue) {
   // Open a file with four annotations and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_stamp_with_ap.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
 
   static constexpr char kDateKey[] = "M";
@@ -934,7 +943,7 @@ TEST_F(FPDFAnnotEmbeddertest, GetSetStringValue) {
 
   // Save the document, closing the page and document.
   EXPECT_TRUE(FPDF_SaveAsCopy(document(), this, 0));
-  FPDF_ClosePage(page);
+  UnloadPage(page);
 
   // Open the saved annotation.
 #if _FX_PLATFORM_ == _FX_PLATFORM_APPLE_
@@ -967,7 +976,7 @@ TEST_F(FPDFAnnotEmbeddertest, GetSetStringValue) {
 TEST_F(FPDFAnnotEmbeddertest, GetSetAP) {
   // Open a file with four annotations and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_stamp_with_ap.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
 
   {
@@ -1064,7 +1073,7 @@ TEST_F(FPDFAnnotEmbeddertest, GetSetAP) {
 
   // Save the modified document, then reopen it.
   EXPECT_TRUE(FPDF_SaveAsCopy(document(), this, 0));
-  FPDF_ClosePage(page);
+  UnloadPage(page);
 
   OpenSavedDocument();
   page = LoadSavedPage(0);
@@ -1092,7 +1101,7 @@ TEST_F(FPDFAnnotEmbeddertest, GetSetAP) {
 TEST_F(FPDFAnnotEmbeddertest, RemoveOptionalAP) {
   // Open a file with four annotations and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_stamp_with_ap.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
 
   {
@@ -1123,13 +1132,13 @@ TEST_F(FPDFAnnotEmbeddertest, RemoveOptionalAP) {
                                   nullptr, 0));
   }
 
-  FPDF_ClosePage(page);
+  UnloadPage(page);
 }
 
 TEST_F(FPDFAnnotEmbeddertest, RemoveRequiredAP) {
   // Open a file with four annotations and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_stamp_with_ap.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
 
   {
@@ -1158,13 +1167,13 @@ TEST_F(FPDFAnnotEmbeddertest, RemoveRequiredAP) {
                                   nullptr, 0));
   }
 
-  FPDF_ClosePage(page);
+  UnloadPage(page);
 }
 
 TEST_F(FPDFAnnotEmbeddertest, ExtractLinkedAnnotations) {
   // Open a file with annotations and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_highlight_square_with_ap.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
   EXPECT_EQ(-1, FPDFPage_GetAnnotIndex(page, nullptr));
 
@@ -1212,7 +1221,7 @@ TEST_F(FPDFAnnotEmbeddertest, ExtractLinkedAnnotations) {
 TEST_F(FPDFAnnotEmbeddertest, GetFormFieldFlagsTextField) {
   // Open file with form text fields.
   ASSERT_TRUE(OpenDocument("text_form_multiple.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
 
   {
@@ -1243,7 +1252,7 @@ TEST_F(FPDFAnnotEmbeddertest, GetFormFieldFlagsTextField) {
 TEST_F(FPDFAnnotEmbeddertest, GetFormFieldFlagsComboBox) {
   // Open file with form text fields.
   ASSERT_TRUE(OpenDocument("combobox_form.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
 
   {
diff --git a/fpdfsdk/fpdfdoc_embeddertest.cpp b/fpdfsdk/fpdfdoc_embeddertest.cpp
index abe3d8c646..7cd27751e7 100644
--- a/fpdfsdk/fpdfdoc_embeddertest.cpp
+++ b/fpdfsdk/fpdfdoc_embeddertest.cpp
@@ -146,7 +146,7 @@ TEST_F(FPDFDocEmbeddertest, BUG_680376) {
 TEST_F(FPDFDocEmbeddertest, ActionGetFilePath) {
   EXPECT_TRUE(OpenDocument("launch_action.pdf"));
 
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
 
   // The target action is nearly the size of the whole page.
@@ -165,7 +165,7 @@ TEST_F(FPDFDocEmbeddertest, ActionGetFilePath) {
   EXPECT_EQ(bufsize, FPDFAction_GetFilePath(action, buf, bufsize));
   EXPECT_EQ(std::string(kExpectedResult), std::string(buf));
 
-  FPDF_ClosePage(page);
+  UnloadPage(page);
 }
 
 TEST_F(FPDFDocEmbeddertest, NoBookmarks) {
diff --git a/fpdfsdk/fpdfedit_embeddertest.cpp b/fpdfsdk/fpdfedit_embeddertest.cpp
index f388107708..f27cf747c1 100644
--- a/fpdfsdk/fpdfedit_embeddertest.cpp
+++ b/fpdfsdk/fpdfedit_embeddertest.cpp
@@ -926,7 +926,7 @@ TEST_F(FPDFEditEmbeddertest, AddTrueTypeFontText) {
 TEST_F(FPDFEditEmbeddertest, TransformAnnot) {
   // Open a file with one annotation and load its first page.
   ASSERT_TRUE(OpenDocument("annotation_highlight_long_content.pdf"));
-  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  FPDF_PAGE page = LoadPage(0);
   ASSERT_TRUE(page);
 
   {
diff --git a/fpdfsdk/fpdfppo_embeddertest.cpp b/fpdfsdk/fpdfppo_embeddertest.cpp
index 0b3463e391..4e7b2ae82e 100644
--- a/fpdfsdk/fpdfppo_embeddertest.cpp
+++ b/fpdfsdk/fpdfppo_embeddertest.cpp
@@ -261,7 +261,7 @@ TEST_F(FPDFPPOEmbeddertest, ImportWithZeroLengthStream) {
 
   std::string digest = HashBitmap(bitmap);
   FPDFBitmap_Destroy(bitmap);
-  FPDF_ClosePage(page);
+  UnloadPage(page);
 
   FPDF_DOCUMENT new_doc = FPDF_CreateNewDocument();
   EXPECT_TRUE(new_doc);
diff --git a/testing/embedder_test.cpp b/testing/embedder_test.cpp
index bd52c26286..32c761e050 100644
--- a/testing/embedder_test.cpp
+++ b/testing/embedder_test.cpp
@@ -22,7 +22,9 @@
 #include "testing/image_diff/image_diff_png.h"
 #include "testing/test_support.h"
 #include "testing/utils/path_service.h"
+#include "third_party/base/logging.h"
 #include "third_party/base/ptr_util.h"
+#include "third_party/base/stl_util.h"
 
 #ifdef PDF_ENABLE_V8
 #include "v8/include/v8-platform.h"
@@ -76,6 +78,10 @@ void EmbedderTest::SetUp() {
 }
 
 void EmbedderTest::TearDown() {
+  // Use an EXPECT_EQ() here and continue to let TearDown() finish as cleanly as
+  // possible. This can fail when an ASSERT test fails in a test case.
+  EXPECT_EQ(0U, page_map_.size());
+
   if (document_) {
     FORM_DoDocumentAAction(form_handle_, FPDFDOC_AACTION_WC);
     FPDFDOC_ExitFormFillEnvironment(form_handle_);
@@ -245,10 +251,8 @@ int EmbedderTest::GetPageCount() {
 
 FPDF_PAGE EmbedderTest::LoadPage(int page_number) {
   ASSERT(form_handle_);
-  // First check whether it is loaded already.
-  auto it = page_map_.find(page_number);
-  if (it != page_map_.end())
-    return it->second;
+  ASSERT(page_number >= 0);
+  ASSERT(!pdfium::ContainsKey(page_map_, page_number));
 
   FPDF_PAGE page = FPDF_LoadPage(document_, page_number);
   if (!page)
@@ -258,22 +262,23 @@ FPDF_PAGE EmbedderTest::LoadPage(int page_number) {
   FORM_DoPageAAction(page, form_handle_, FPDFPAGE_AACTION_OPEN);
   // Cache the page.
   page_map_[page_number] = page;
-  page_reverse_map_[page] = page_number;
   return page;
 }
 
 void EmbedderTest::UnloadPage(FPDF_PAGE page) {
   ASSERT(form_handle_);
+
+  int page_number = GetPageNumberForLoadedPage(page);
+  if (page_number < 0) {
+    NOTREACHED();
+    return;
+  }
+
   FORM_DoPageAAction(page, form_handle_, FPDFPAGE_AACTION_CLOSE);
   FORM_OnBeforeClosePage(page, form_handle_);
   FPDF_ClosePage(page);
 
-  auto it = page_reverse_map_.find(page);
-  if (it == page_reverse_map_.end())
-    return;
-
-  page_map_.erase(it->second);
-  page_reverse_map_.erase(it);
+  page_map_.erase(page_number);
 }
 
 FPDF_BITMAP EmbedderTest::RenderPageDeprecated(FPDF_PAGE page) {
@@ -287,6 +292,10 @@ std::unique_ptr<void, FPDFBitmapDeleter> EmbedderTest::RenderLoadedPage(
 
 std::unique_ptr<void, FPDFBitmapDeleter>
 EmbedderTest::RenderLoadedPageWithFlags(FPDF_PAGE page, int flags) {
+  if (GetPageNumberForLoadedPage(page) < 0) {
+    NOTREACHED();
+    return nullptr;
+  }
   return RenderPageWithFlags(page, form_handle_, flags);
 }
 
@@ -521,3 +530,14 @@ int EmbedderTest::GetBlockFromString(void* param,
   memcpy(buf, new_file->data() + pos, size);
   return 1;
 }
+
+int EmbedderTest::GetPageNumberForLoadedPage(FPDF_PAGE page) const {
+  for (const auto& it : page_map_) {
+    if (it.second == page) {
+      int page_number = it.first;
+      ASSERT(page_number >= 0);
+      return page_number;
+    }
+  }
+  return -1;
+}
diff --git a/testing/embedder_test.h b/testing/embedder_test.h
index 18b16b7066..c8fce4825f 100644
--- a/testing/embedder_test.h
+++ b/testing/embedder_test.h
@@ -106,11 +106,17 @@ class EmbedderTest : public ::testing::Test,
   int GetFirstPageNum();
   int GetPageCount();
 
-  // Load a specific page of the open document.
+  // Load a specific page of the open document with a given non-negative
+  // |page_number|. On success, fire form events for the page and return a page
+  // handle. On failure, return nullptr.
+  // The caller does not own the returned page handle, but must call
+  // UnloadPage() on it when done.
+  // The caller cannot call this for a |page_number| if it already obtained and
+  // holds the page handle for that page.
   FPDF_PAGE LoadPage(int page_number);
 
-  // Release the resources obtained from LoadPage(). Further use of |page|
-  // is prohibited after this call is made.
+  // Fire form unload events and release the resources for a |page| obtained
+  // from LoadPage(). Further use of |page| is prohibited after calling this.
   void UnloadPage(FPDF_PAGE page);
 
   // Convert a loaded page into a bitmap.
@@ -215,7 +221,6 @@ class EmbedderTest : public ::testing::Test,
   size_t file_length_ = 0;
   std::unique_ptr<char, pdfium::FreeDeleter> file_contents_;
   std::map<int, FPDF_PAGE> page_map_;
-  std::map<FPDF_PAGE, int> page_reverse_map_;
 
   FPDF_DOCUMENT saved_document_ = nullptr;
   FPDF_FORMHANDLE saved_form_handle_ = nullptr;
@@ -242,6 +247,10 @@ class EmbedderTest : public ::testing::Test,
                                 const void* data,
                                 unsigned long size);
 
+  // Find |page| inside |page_map_| and return the associated page number, or -1
+  // if |page| cannot be found.
+  int GetPageNumberForLoadedPage(FPDF_PAGE page) const;
+
   std::string data_string_;
 };