AK: Consolidate iterators for HashTable and DoublyLinkedList respectively.

Get rid of the ConstIterator classes for these containers and use templated
FooIterator<T, ...> and FooIterator<const T, ...> helpers.

This makes the HashTable class a lot easier to read.

AK/Tests/.gitignore

@@ -1,5 +1,6 @@
 TestString
 TestQueue
 TestVector
+TestHashMap
 *.d
 *.o

AK/Tests/Makefile

@@ -1,4 +1,6 @@
-all: TestString TestQueue TestVector
+PROGRAMS = TestString TestQueue TestVector TestHashMap
+
+all: $(PROGRAMS)
 
 CXXFLAGS = -std=c++17 -Wall -Wextra
 
@@ -11,5 +13,8 @@ TestQueue: TestQueue.cpp ../String.cpp ../StringImpl.cpp ../StringBuilder.cpp ..
 TestVector: TestVector.cpp ../String.cpp ../StringImpl.cpp ../StringBuilder.cpp ../StringView.cpp TestHelpers.h
 	$(CXX) $(CXXFLAGS) -I../ -I../../ -o $@ TestVector.cpp ../String.cpp ../StringImpl.cpp ../StringBuilder.cpp ../StringView.cpp
 
+TestHashMap: TestHashMap.cpp ../String.cpp ../StringImpl.cpp ../StringBuilder.cpp ../StringView.cpp TestHelpers.h
+	$(CXX) $(CXXFLAGS) -I../ -I../../ -o $@ TestHashMap.cpp ../String.cpp ../StringImpl.cpp ../StringBuilder.cpp ../StringView.cpp
+
 clean:
-	rm -f TestString TestQueue
+	rm -f $(PROGRAMS)

AK/Tests/TestHashMap.cpp

@@ -0,0 +1,28 @@
+#include "TestHelpers.h"
+#include <AK/AKString.h>
+#include <AK/HashMap.h>
+
+typedef HashMap<int, int> IntIntMap;
+
+int main()
+{
+    EXPECT(IntIntMap().is_empty());
+    EXPECT(IntIntMap().size() == 0);
+
+    HashMap<int, String> number_to_string;
+    number_to_string.set(1, "One");
+    number_to_string.set(2, "Two");
+    number_to_string.set(3, "Three");
+    
+    EXPECT_EQ(number_to_string.is_empty(), false);
+    EXPECT_EQ(number_to_string.size(), 3);
+
+    int loop_counter = 0;
+    for (auto& it : number_to_string) {
+        EXPECT(!it.value.is_null());
+        ++loop_counter;
+    }
+
+    EXPECT_EQ(loop_counter, 3);
+    return 0;
+}