add unit test for coalescing erase change units within a change operation

test/src/test_Buffer.cc

@@ -242,3 +242,27 @@ TEST(BufferTest, allows_undo_and_redo_of_erases)
     EXPECT_EQ(ss("bc\ndfghi\n"), b.get_string());
     EXPECT_EQ(C('f'), **it);
 }
+
+TEST(BufferTest, erase_chunks_are_coalesced_within_a_change_operation)
+{
+    std::string s("abcdef\n");
+    Buffer b((const uint8_t *)&s[0], s.size());
+    auto it = b.add_cursor();
+
+    b.enter_insert_mode();
+    it->go_right_in_line(false);
+    it->go_right_in_line(false); /* erase just after previous erase */
+    b.erase_code_point(*it);
+    b.erase_code_point(*it);
+    it->go_left_in_line();
+    b.erase_code_point(*it); /* erase just before previous erase */
+    b.exit_insert_mode();
+    EXPECT_EQ(C('e'), **it);
+    EXPECT_EQ(ss("aef\n"), b.get_string());
+    ASSERT_EQ(1u, b.m_change_operations.size());
+    ASSERT_EQ(1u, b.m_change_operations[0]->changes.size());
+
+    b.undo();
+    EXPECT_EQ(C('e'), **it);
+    EXPECT_EQ(ss("abcdef\n"), b.get_string());
+}