diff --git a/src/core/GapBuffer.cc b/src/core/GapBuffer.cc
index 0c17ca3..cb7fc04 100644
--- a/src/core/GapBuffer.cc
+++ b/src/core/GapBuffer.cc
@@ -70,5 +70,6 @@ void GapBuffer::move_gap(size_t position)
         {
             memmove(&m_buffer[m_gap_position], &m_buffer[m_gap_position + gap_size()], position - m_gap_position);
         }
+        m_gap_position = position;
     }
 }
diff --git a/test/src/test_GapBuffer.cc b/test/src/test_GapBuffer.cc
new file mode 100644
index 0000000..2d18e58
--- /dev/null
+++ b/test/src/test_GapBuffer.cc
@@ -0,0 +1,39 @@
+#include "gtest/gtest.h"
+#include "GapBuffer.h"
+#include "System.h"
+
+TEST(GapBufferTest, creates_an_empty_buffer)
+{
+    GapBuffer gp;
+    EXPECT_EQ(0u, gp.size());
+}
+
+TEST(GapBufferTest, creates_a_buffer_from_preallocated_memory)
+{
+    uint8_t * b = (uint8_t *)System::alloc_pages(2u);
+    strcpy((char *)b, "hi\n");
+    GapBuffer gp(b, System::page_size * 2u, 3u);
+
+    EXPECT_EQ(3u, gp.size());
+}
+
+TEST(GapBufferTest, allows_inserting)
+{
+    GapBuffer gp;
+
+    gp.insert(0u, (const uint8_t *)"test", 4u);
+    EXPECT_EQ("test", gp.get_string());
+    EXPECT_EQ(4u, gp.size());
+
+    gp.insert(2u, (const uint8_t *)"12", 2u);
+    EXPECT_EQ("te12st", gp.get_string());
+    EXPECT_EQ(6u, gp.size());
+
+    gp.insert(0u, (const uint8_t *)"-", 1u);
+    EXPECT_EQ("-te12st", gp.get_string());
+    EXPECT_EQ(7u, gp.size());
+
+    gp.insert(7u, (const uint8_t *)"!", 1u);
+    EXPECT_EQ("-te12st!", gp.get_string());
+    EXPECT_EQ(8u, gp.size());
+}