Port Firestore Document to C++ (#777)

* implement SnapshotVersion and test

* update project

* implement MaybeDocument and test

* move snapshot-version from core to model

* fix a bug

* implement Document and test

* implement NoDocument

* adding type tag and fix style

* fix a few bugs, discovered after merging and test run.

* add assert to check FieldValue type and more test for comparision.

* address changes

* allow moving FieldValue to construct Document.

* address changes

* add document tests to project

* use std::less convention

* make Type::Unknown static initializer

12 files changed, 545 insertions, 3 deletions

diff --git a/Firestore/Example/Firestore.xcodeproj/project.pbxproj b/Firestore/Example/Firestore.xcodeproj/project.pbxproj
index e3f9800..3b91c76 100644
--- a/Firestore/Example/Firestore.xcodeproj/project.pbxproj
+++ b/Firestore/Example/Firestore.xcodeproj/project.pbxproj
@@ -140,6 +140,9 @@
 		AB380D02201BC69F00D97691 /* bits_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = AB380D01201BC69F00D97691 /* bits_test.cc */; };
 		AB380D04201BC6E400D97691 /* ordered_code_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = AB380D03201BC6E400D97691 /* ordered_code_test.cc */; };
 		AB38D93020236E21000A432D /* database_info_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = AB38D92E20235D22000A432D /* database_info_test.cc */; };
+		AB6B908420322E4D00CC290A /* document_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = AB6B908320322E4D00CC290A /* document_test.cc */; };
+		AB6B908620322E6D00CC290A /* maybe_document_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = AB6B908520322E6D00CC290A /* maybe_document_test.cc */; };
+		AB6B908820322E8800CC290A /* no_document_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = AB6B908720322E8800CC290A /* no_document_test.cc */; };
 		AB7BAB342012B519001E0872 /* geo_point_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = AB7BAB332012B519001E0872 /* geo_point_test.cc */; };
 		ABA495BB202B7E80008A7851 /* snapshot_version_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = ABA495B9202B7E79008A7851 /* snapshot_version_test.cc */; };
 		ABC1D7DC2023A04B00BA84F0 /* credentials_provider_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = AB38D9342023966E000A432D /* credentials_provider_test.cc */; };
@@ -346,6 +349,9 @@
 		AB38D93220239654000A432D /* user_test.cc */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = user_test.cc; sourceTree = "<group>"; };
 		AB38D9342023966E000A432D /* credentials_provider_test.cc */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = credentials_provider_test.cc; sourceTree = "<group>"; };
 		AB38D93620239689000A432D /* empty_credentials_provider_test.cc */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = empty_credentials_provider_test.cc; sourceTree = "<group>"; };
+		AB6B908320322E4D00CC290A /* document_test.cc */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = document_test.cc; sourceTree = "<group>"; };
+		AB6B908520322E6D00CC290A /* maybe_document_test.cc */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = maybe_document_test.cc; sourceTree = "<group>"; };
+		AB6B908720322E8800CC290A /* no_document_test.cc */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = no_document_test.cc; sourceTree = "<group>"; };
 		AB71064B201FA60300344F18 /* database_id_test.cc */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = database_id_test.cc; sourceTree = "<group>"; };
 		AB7BAB332012B519001E0872 /* geo_point_test.cc */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = geo_point_test.cc; path = ../../core/test/firebase/firestore/geo_point_test.cc; sourceTree = "<group>"; };
 		ABA495B9202B7E79008A7851 /* snapshot_version_test.cc */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = snapshot_version_test.cc; sourceTree = "<group>"; };
@@ -585,10 +591,13 @@
 			isa = PBXGroup;
 			children = (
 				B6152AD5202A5385000E5744 /* document_key_test.cc */,
+				AB6B908320322E4D00CC290A /* document_test.cc */,
 				B686F2B02024FFD70028D6BE /* resource_path_test.cc */,
 				B686F2AD2023DDB20028D6BE /* field_path_test.cc */,
 				AB71064B201FA60300344F18 /* database_id_test.cc */,
 				AB356EF6200EA5EB0089B766 /* field_value_test.cc */,
+				AB6B908520322E6D00CC290A /* maybe_document_test.cc */,
+				AB6B908720322E8800CC290A /* no_document_test.cc */,
 				ABA495B9202B7E79008A7851 /* snapshot_version_test.cc */,
 				ABF6506B201131F8005F2C74 /* timestamp_test.cc */,
 			);
@@ -1310,6 +1319,7 @@
 				5492E0AD2021552D00B64F25 /* FSTMemoryMutationQueueTests.mm in Sources */,
 				5492E051202154AA00B64F25 /* FIRQueryTests.mm in Sources */,
 				5492E054202154AB00B64F25 /* FIRFieldValueTests.mm in Sources */,
+				AB6B908620322E6D00CC290A /* maybe_document_test.cc in Sources */,
 				5492E09F2021552D00B64F25 /* FSTLevelDBMigrationsTests.mm in Sources */,
 				5492E053202154AB00B64F25 /* FIRDocumentReferenceTests.mm in Sources */,
 				5492E09D2021552D00B64F25 /* FSTLocalStoreTests.mm in Sources */,
@@ -1317,6 +1327,7 @@
 				5492E0A72021552D00B64F25 /* FSTLevelDBKeyTests.mm in Sources */,
 				5492E0A22021552D00B64F25 /* FSTQueryCacheTests.mm in Sources */,
 				5492E0A52021552D00B64F25 /* FSTMemoryRemoteDocumentCacheTests.mm in Sources */,
+				AB6B908820322E8800CC290A /* no_document_test.cc in Sources */,
 				5492E0BD2021555100B64F25 /* FSTDocumentTests.mm in Sources */,
 				5492E0B92021555100B64F25 /* FSTDocumentKeyTests.mm in Sources */,
 				DE2EF0871F3D0B6E003D0CDC /* FSTImmutableSortedSet+Testing.m in Sources */,
@@ -1331,6 +1342,7 @@
 				5492E0AB2021552D00B64F25 /* StringViewTests.mm in Sources */,
 				5492E0C92021557E00B64F25 /* FSTRemoteEventTests.mm in Sources */,
 				ABC1D7E42024AFDE00BA84F0 /* firebase_credentials_provider_test.mm in Sources */,
+				AB6B908420322E4D00CC290A /* document_test.cc in Sources */,
 				ABF6506C201131F8005F2C74 /* timestamp_test.cc in Sources */,
 				5492E0AE2021552D00B64F25 /* FSTLevelDBQueryCacheTests.mm in Sources */,
 				ABC1D7DC2023A04B00BA84F0 /* credentials_provider_test.cc in Sources */,
diff --git a/Firestore/core/src/firebase/firestore/model/CMakeLists.txt b/Firestore/core/src/firebase/firestore/model/CMakeLists.txt
index 95310ec..1b0e6a4 100644
--- a/Firestore/core/src/firebase/firestore/model/CMakeLists.txt
+++ b/Firestore/core/src/firebase/firestore/model/CMakeLists.txt
@@ -18,16 +18,22 @@ cc_library(
     base_path.h
     database_id.cc
     database_id.h
+    document.cc
+    document.h
     document_key.cc
     document_key.h
     field_path.cc
     field_path.h
     field_value.cc
     field_value.h
-    snapshot_version.cc
-    snapshot_version.h
+    maybe_document.cc
+    maybe_document.h
+    no_document.cc
+    no_document.h
     resource_path.cc
     resource_path.h
+    snapshot_version.cc
+    snapshot_version.h
     timestamp.cc
     timestamp.h
   DEPENDS
diff --git a/Firestore/core/src/firebase/firestore/model/document.cc b/Firestore/core/src/firebase/firestore/model/document.cc
new file mode 100644
index 0000000..16548cd
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/model/document.cc
@@ -0,0 +1,50 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Firestore/core/src/firebase/firestore/model/document.h"
+
+#include <utility>
+
+#include "Firestore/core/src/firebase/firestore/util/firebase_assert.h"
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+Document::Document(FieldValue&& data,
+                   DocumentKey key,
+                   SnapshotVersion version,
+                   bool has_local_mutations)
+    : MaybeDocument(std::move(key), std::move(version)),
+      data_(std::move(data)),
+      has_local_mutations_(has_local_mutations) {
+  set_type(Type::Document);
+  FIREBASE_ASSERT(FieldValue::Type::Object == data.type());
+}
+
+bool Document::Equals(const MaybeDocument& other) const {
+  if (other.type() != Type::Document) {
+    return false;
+  }
+  const Document& other_doc = static_cast<const Document&>(other);
+  return MaybeDocument::Equals(other) &&
+         has_local_mutations_ == other_doc.has_local_mutations_ &&
+         data_ == other_doc.data_;
+}
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase
diff --git a/Firestore/core/src/firebase/firestore/model/document.h b/Firestore/core/src/firebase/firestore/model/document.h
new file mode 100644
index 0000000..50a7b90
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/model/document.h
@@ -0,0 +1,72 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_DOCUMENT_H_
+#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_DOCUMENT_H_
+
+#include "Firestore/core/src/firebase/firestore/model/field_value.h"
+#include "Firestore/core/src/firebase/firestore/model/maybe_document.h"
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+/**
+ * Represents a document in Firestore with a key, version, data and whether the
+ * data has local mutations applied to it.
+ */
+class Document : public MaybeDocument {
+ public:
+  /**
+   * Construct a document. FieldValue must be passed by rvalue.
+   */
+  Document(FieldValue&& data,
+           DocumentKey key,
+           SnapshotVersion version,
+           bool has_local_mutations);
+
+  const FieldValue& data() const {
+    return data_;
+  }
+
+  bool has_local_mutations() const {
+    return has_local_mutations_;
+  }
+
+ protected:
+  bool Equals(const MaybeDocument& other) const override;
+
+ private:
+  FieldValue data_;  // This is of type Object.
+  bool has_local_mutations_;
+};
+
+/** Compares against another Document. */
+inline bool operator==(const Document& lhs, const Document& rhs) {
+  return lhs.version() == rhs.version() && lhs.key() == rhs.key() &&
+         lhs.has_local_mutations() == rhs.has_local_mutations() &&
+         lhs.data() == rhs.data();
+}
+
+inline bool operator!=(const Document& lhs, const Document& rhs) {
+  return !(lhs == rhs);
+}
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_DOCUMENT_H_
diff --git a/Firestore/core/src/firebase/firestore/model/maybe_document.cc b/Firestore/core/src/firebase/firestore/model/maybe_document.cc
new file mode 100644
index 0000000..4f3be1d
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/model/maybe_document.cc
@@ -0,0 +1,38 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Firestore/core/src/firebase/firestore/model/maybe_document.h"
+
+#include <utility>
+
+#include "Firestore/core/src/firebase/firestore/util/firebase_assert.h"
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+MaybeDocument::MaybeDocument(DocumentKey key, SnapshotVersion version)
+    : key_(std::move(key)), version_(std::move(version)) {
+}
+
+bool MaybeDocument::Equals(const MaybeDocument& other) const {
+  return type_ == other.type_ && version_ == other.version_ &&
+         key_ == other.key_;
+}
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase
diff --git a/Firestore/core/src/firebase/firestore/model/maybe_document.h b/Firestore/core/src/firebase/firestore/model/maybe_document.h
new file mode 100644
index 0000000..71bd3ef
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/model/maybe_document.h
@@ -0,0 +1,100 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_MAYBE_DOCUMENT_H_
+#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_MAYBE_DOCUMENT_H_
+
+#include <functional>
+
+#include "Firestore/core/src/firebase/firestore/model/document_key.h"
+#include "Firestore/core/src/firebase/firestore/model/snapshot_version.h"
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+/**
+ * The result of a lookup for a given path may be an existing document or a
+ * tombstone that marks the path deleted.
+ */
+class MaybeDocument {
+ public:
+  /**
+   * All the different kinds of documents, including MaybeDocument and its
+   * subclasses. This is used to provide RTTI for documents.
+   */
+  enum class Type {
+    Unknown,
+    Document,
+    NoDocument,
+  };
+
+  MaybeDocument(DocumentKey key, SnapshotVersion version);
+
+  /** The runtime type of this document. */
+  Type type() const {
+    return type_;
+  }
+
+  /** The key for this document. */
+  const DocumentKey& key() const {
+    return key_;
+  }
+
+  /**
+   * Returns the version of this document if it exists or a version at which
+   * this document was guaranteed to not exist.
+   */
+  const SnapshotVersion& version() const {
+    return version_;
+  }
+
+ protected:
+  // Only allow subclass to set their types.
+  void set_type(Type type) {
+    type_ = type;
+  }
+
+  virtual bool Equals(const MaybeDocument& other) const;
+
+  friend bool operator==(const MaybeDocument& lhs, const MaybeDocument& rhs);
+
+ private:
+  Type type_ = Type::Unknown;
+  DocumentKey key_;
+  SnapshotVersion version_;
+};
+
+inline bool operator==(const MaybeDocument& lhs, const MaybeDocument& rhs) {
+  return lhs.Equals(rhs);
+}
+
+inline bool operator!=(const MaybeDocument& lhs, const MaybeDocument& rhs) {
+  return !(lhs == rhs);
+}
+
+/** Compares against another MaybeDocument by keys only. */
+struct DocumentKeyComparator : public std::less<MaybeDocument> {
+  bool operator()(const MaybeDocument& lhs, const MaybeDocument& rhs) const {
+    return lhs.key() < rhs.key();
+  }
+};
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_MAYBE_DOCUMENT_H_
diff --git a/Firestore/core/src/firebase/firestore/model/no_document.cc b/Firestore/core/src/firebase/firestore/model/no_document.cc
new file mode 100644
index 0000000..98cb428
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/model/no_document.cc
@@ -0,0 +1,32 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Firestore/core/src/firebase/firestore/model/no_document.h"
+
+#include <utility>
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+NoDocument::NoDocument(DocumentKey key, SnapshotVersion version)
+    : MaybeDocument(std::move(key), std::move(version)) {
+  set_type(Type::NoDocument);
+}
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase
diff --git a/Firestore/core/src/firebase/firestore/model/no_document.h b/Firestore/core/src/firebase/firestore/model/no_document.h
new file mode 100644
index 0000000..7cfd47c
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/model/no_document.h
@@ -0,0 +1,36 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_NO_DOCUMENT_H_
+#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_NO_DOCUMENT_H_
+
+#include "Firestore/core/src/firebase/firestore/model/maybe_document.h"
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+/** Represents that no documents exists for the key at the given version. */
+class NoDocument : public MaybeDocument {
+ public:
+  NoDocument(DocumentKey key, SnapshotVersion version);
+};
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_NO_DOCUMENT_H_
diff --git a/Firestore/core/test/firebase/firestore/model/CMakeLists.txt b/Firestore/core/test/firebase/firestore/model/CMakeLists.txt
index e73be98..0d581bc 100644
--- a/Firestore/core/test/firebase/firestore/model/CMakeLists.txt
+++ b/Firestore/core/test/firebase/firestore/model/CMakeLists.txt
@@ -17,11 +17,14 @@ cc_test(
   SOURCES
     database_id_test.cc
     document_key_test.cc
+    document_test.cc
     field_path_test.cc
     field_value_test.cc
+    maybe_document_test.cc
+    no_document_test.cc
+    resource_path_test.cc
     snapshot_version_test.cc
     timestamp_test.cc
-    resource_path_test.cc
   DEPENDS
     firebase_firestore_model
 )
diff --git a/Firestore/core/test/firebase/firestore/model/document_test.cc b/Firestore/core/test/firebase/firestore/model/document_test.cc
new file mode 100644
index 0000000..6b72360
--- /dev/null
+++ b/Firestore/core/test/firebase/firestore/model/document_test.cc
@@ -0,0 +1,76 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Firestore/core/src/firebase/firestore/model/document.h"
+
+#include "absl/strings/string_view.h"
+#include "gtest/gtest.h"
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+namespace {
+
+inline Document MakeDocument(const absl::string_view data,
+                             const absl::string_view path,
+                             const Timestamp& timestamp,
+                             bool has_local_mutations) {
+  return Document(FieldValue::ObjectValue(
+                      {{"field", FieldValue::StringValue(data.data())}}),
+                  DocumentKey::FromPathString(path.data()),
+                  SnapshotVersion(timestamp), has_local_mutations);
+}
+
+}  // anonymous namespace
+
+TEST(Document, Getter) {
+  const Document& doc =
+      MakeDocument("foo", "i/am/a/path", Timestamp(123, 456), true);
+  EXPECT_EQ(MaybeDocument::Type::Document, doc.type());
+  EXPECT_EQ(
+      FieldValue::ObjectValue({{"field", FieldValue::StringValue("foo")}}),
+      doc.data());
+  EXPECT_EQ(DocumentKey::FromPathString("i/am/a/path"), doc.key());
+  EXPECT_EQ(SnapshotVersion(Timestamp(123, 456)), doc.version());
+  EXPECT_TRUE(doc.has_local_mutations());
+}
+
+TEST(Document, Comparison) {
+  EXPECT_EQ(MakeDocument("foo", "i/am/a/path", Timestamp(123, 456), true),
+            MakeDocument("foo", "i/am/a/path", Timestamp(123, 456), true));
+  EXPECT_NE(MakeDocument("foo", "i/am/a/path", Timestamp(123, 456), true),
+            MakeDocument("bar", "i/am/a/path", Timestamp(123, 456), true));
+  EXPECT_NE(
+      MakeDocument("foo", "i/am/a/path", Timestamp(123, 456), true),
+      MakeDocument("foo", "i/am/another/path", Timestamp(123, 456), true));
+  EXPECT_NE(MakeDocument("foo", "i/am/a/path", Timestamp(123, 456), true),
+            MakeDocument("foo", "i/am/a/path", Timestamp(456, 123), true));
+  EXPECT_NE(MakeDocument("foo", "i/am/a/path", Timestamp(123, 456), true),
+            MakeDocument("foo", "i/am/a/path", Timestamp(123, 456), false));
+
+  // Document and MaybeDocument will not equal. In particular, Document and
+  // NoDocument will not equal, which I won't test here.
+  EXPECT_NE(Document(FieldValue::ObjectValue({}),
+                     DocumentKey::FromPathString("same/path"),
+                     SnapshotVersion(Timestamp()), false),
+            MaybeDocument(DocumentKey::FromPathString("same/path"),
+                          SnapshotVersion(Timestamp())));
+}
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase
diff --git a/Firestore/core/test/firebase/firestore/model/maybe_document_test.cc b/Firestore/core/test/firebase/firestore/model/maybe_document_test.cc
new file mode 100644
index 0000000..005798a
--- /dev/null
+++ b/Firestore/core/test/firebase/firestore/model/maybe_document_test.cc
@@ -0,0 +1,66 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Firestore/core/src/firebase/firestore/model/maybe_document.h"
+
+#include "absl/strings/string_view.h"
+#include "gtest/gtest.h"
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+namespace {
+
+inline MaybeDocument MakeMaybeDocument(const absl::string_view path,
+                                       const Timestamp& timestamp) {
+  return MaybeDocument(DocumentKey::FromPathString(path.data()),
+                       SnapshotVersion(timestamp));
+}
+
+inline bool operator<(const MaybeDocument& lhs, const MaybeDocument& rhs) {
+  static const DocumentKeyComparator less;
+  return less(lhs, rhs);
+}
+
+}  // anonymous namespace
+
+TEST(MaybeDocument, Getter) {
+  const MaybeDocument& doc =
+      MakeMaybeDocument("i/am/a/path", Timestamp(123, 456));
+  EXPECT_EQ(MaybeDocument::Type::Unknown, doc.type());
+  EXPECT_EQ(DocumentKey::FromPathString("i/am/a/path"), doc.key());
+  EXPECT_EQ(SnapshotVersion(Timestamp(123, 456)), doc.version());
+}
+
+TEST(MaybeDocument, Comparison) {
+  EXPECT_TRUE(MakeMaybeDocument("root/123", Timestamp(456, 123)) <
+              MakeMaybeDocument("root/456", Timestamp(123, 456)));
+  // MaybeDocument comparision is purely key-based.
+  EXPECT_FALSE(MakeMaybeDocument("root/123", Timestamp(111, 111)) <
+               MakeMaybeDocument("root/123", Timestamp(222, 222)));
+
+  EXPECT_EQ(MakeMaybeDocument("root/123", Timestamp(456, 123)),
+            MakeMaybeDocument("root/123", Timestamp(456, 123)));
+  EXPECT_NE(MakeMaybeDocument("root/123", Timestamp(456, 123)),
+            MakeMaybeDocument("root/456", Timestamp(456, 123)));
+  EXPECT_NE(MakeMaybeDocument("root/123", Timestamp(456, 123)),
+            MakeMaybeDocument("root/123", Timestamp(123, 456)));
+}
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase
diff --git a/Firestore/core/test/firebase/firestore/model/no_document_test.cc b/Firestore/core/test/firebase/firestore/model/no_document_test.cc
new file mode 100644
index 0000000..825820f
--- /dev/null
+++ b/Firestore/core/test/firebase/firestore/model/no_document_test.cc
@@ -0,0 +1,51 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Firestore/core/src/firebase/firestore/model/no_document.h"
+
+#include "absl/strings/string_view.h"
+#include "gtest/gtest.h"
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+namespace {
+
+inline NoDocument MakeNoDocument(const absl::string_view path,
+                                 const Timestamp& timestamp) {
+  return NoDocument(DocumentKey::FromPathString(path.data()),
+                    SnapshotVersion(timestamp));
+}
+
+}  // anonymous namespace
+
+TEST(NoDocument, Getter) {
+  const NoDocument& doc = MakeNoDocument("i/am/a/path", Timestamp(123, 456));
+  EXPECT_EQ(MaybeDocument::Type::NoDocument, doc.type());
+  EXPECT_EQ(DocumentKey::FromPathString("i/am/a/path"), doc.key());
+  EXPECT_EQ(SnapshotVersion(Timestamp(123, 456)), doc.version());
+
+  // NoDocument and MaybeDocument will not equal.
+  EXPECT_NE(NoDocument(DocumentKey::FromPathString("same/path"),
+                       SnapshotVersion(Timestamp())),
+            MaybeDocument(DocumentKey::FromPathString("same/path"),
+                          SnapshotVersion(Timestamp())));
+}
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase