Add tests for enum attrs tables

ipairs() currently fails due to DFHack#1860

test/structures/enum_attrs.lua

@@ -0,0 +1,78 @@
+function test.getmetatable()
+    expect.eq(getmetatable(df.item_type.attrs), 'item_type.attrs')
+end
+
+local function check_valid_attr_entry(enum_type, index)
+    local entry = enum_type.attrs[index]
+    local suffix = ('%s entry at index %s'):format(enum_type._attr_entry_type, index)
+    expect.ne(entry, nil, 'nil ' .. suffix)
+    expect.true_(enum_type._attr_entry_type:is_instance(entry), 'invalid ' .. suffix)
+end
+
+function test.valid_items()
+    for i in ipairs(df.item_type) do
+        check_valid_attr_entry(df.item_type, i)
+        -- expect.true_(df.item_type.attrs[i])
+        -- expect.true_(df.item_type._attr_entry_type:is_instance(df.item_type.attrs[i]))
+    end
+end
+
+function test.valid_items_name()
+    for i, name in ipairs(df.item_type) do
+        expect.eq(df.item_type.attrs[i], df.item_type.attrs[name])
+    end
+end
+
+function test.valid_items_unique()
+    -- check that every enum item has its own attrs entry
+    local addr_to_name = {}
+    for _, name in ipairs(df.item_type) do
+        local _, addr = df.sizeof(df.item_type.attrs[name])
+        if addr_to_name[addr] then
+            expect.fail(('attrs shared between "%s" and "%s"'):format(name, addr_to_name[name]))
+        else
+            addr_to_name[addr] = name
+        end
+    end
+end
+
+function test.invalid_items()
+    check_valid_attr_entry(df.item_type, df.item_type._first_item - 1)
+    check_valid_attr_entry(df.item_type, df.item_type._last_item + 1)
+end
+
+function test.invalid_items_shared()
+    expect.eq(df.item_type.attrs[df.item_type._first_item - 1], df.item_type.attrs[df.item_type._last_item + 1])
+end
+
+function test.length()
+    expect.eq(#df.item_type.attrs, 0)
+end
+
+local function max_attrs_length(enum_type)
+    return enum_type._last_item - enum_type._first_item + 1
+end
+
+function test.pairs()
+    local i = 0
+    for _ in pairs(df.item_type.attrs) do
+        i = i + 1
+        if i > max_attrs_length(df.item_type) then
+            expect.fail('pairs() returned too many items: ' .. tostring(i))
+            break
+        end
+    end
+    expect.eq(i, 0)
+end
+
+function test.ipairs()
+    local i = 0
+    for _ in ipairs(df.item_type.attrs) do
+        i = i + 1
+        if i > max_attrs_length(df.item_type) then
+            expect.fail('ipairs() returned too many items: ' .. tostring(i))
+            break
+        end
+    end
+    expect.eq(i, max_attrs_length(df.item_type))
+end