diff --git a/tests/files/all_icons.json b/tests/files/all_icons.json
new file mode 100644
index 00000000..3d85f818
--- /dev/null
+++ b/tests/files/all_icons.json
@@ -0,0 +1,114 @@
+[
+    "alert_error",
+    "alert_info",
+    "alert_question",
+    "alert_warn",
+
+    "cls_archive",
+    "cls_character",
+    "cls_custom",
+    "cls_entity",
+    "cls_none",
+    "cls_novel",
+    "cls_object",
+    "cls_plot",
+    "cls_template",
+    "cls_timeline",
+    "cls_trash",
+    "cls_world",
+
+    "prj_folder",
+    "prj_document",
+    "prj_title",
+    "prj_chapter",
+    "prj_scene",
+    "prj_note",
+
+    "fmt_bold",
+    "fmt_italic",
+    "fmt_mark",
+    "fmt_strike",
+    "fmt_subscript",
+    "fmt_superscript",
+    "fmt_underline",
+    "fmt_toolbar",
+
+    "search",
+    "search_cancel",
+    "search_case",
+    "search_loop",
+    "search_preserve",
+    "search_project",
+    "search_regex",
+    "search_replace",
+    "search_word",
+
+    "bullet-off",
+    "bullet-on",
+    "unfold-hide",
+    "unfold-show",
+
+    "sb_build",
+    "sb_details",
+    "sb_novel",
+    "sb_outline",
+    "sb_project",
+    "sb_search",
+    "sb_stats",
+
+    "theme_light",
+    "theme_dark",
+    "theme_auto",
+
+    "add",
+    "bookmarks",
+    "browse",
+    "build_settings",
+    "cancel",
+    "checked",
+    "chevron_down",
+    "chevron_left",
+    "chevron_right",
+    "chevron_up",
+    "close",
+    "copy",
+    "document_add",
+    "document",
+    "edit",
+    "exclude",
+    "export",
+    "filter",
+    "fit_height",
+    "fit_width",
+    "folder",
+    "font",
+    "import",
+    "language",
+    "lines",
+    "list",
+    "margin_bottom",
+    "margin_left",
+    "margin_right",
+    "margin_top",
+    "maximise",
+    "minimise",
+    "more_arrow",
+    "more_vertical",
+    "noncheckable",
+    "open",
+    "panel",
+    "pin",
+    "project_copy",
+    "quote",
+    "refresh",
+    "remove",
+    "revert",
+    "settings",
+    "star",
+    "stats",
+    "text",
+    "timer_off",
+    "timer",
+    "unchecked",
+    "view"
+]
diff --git a/tests/test_gui/test_gui_theme.py b/tests/test_gui/test_gui_theme.py
index 107fd125..d14304d1 100644
--- a/tests/test_gui/test_gui_theme.py
+++ b/tests/test_gui/test_gui_theme.py
@@ -20,6 +20,8 @@ along with this program. If not, see <https://www.gnu.org/licenses/>.
 """
 from __future__ import annotations
 
+import json
+
 from configparser import ConfigParser
 from pathlib import Path
 from unittest.mock import MagicMock, Mock
@@ -563,3 +565,114 @@ def testGuiTheme_LoadDecorations(monkeypatch):
     assert iconCache.getHeaderDecorationNarrow(4)  == iconCache._headerDecNarrow[4]
     assert iconCache.getHeaderDecorationNarrow(5)  == iconCache._headerDecNarrow[5]
     assert iconCache.getHeaderDecorationNarrow(6)  == iconCache._headerDecNarrow[5]
+
+
+THEMES = []
+_listContent(THEMES, CONFIG.assetPath("themes"), ".conf")
+
+
+@pytest.mark.gui
+@pytest.mark.parametrize("theme", [a.stem for a in THEMES])
+def testGuiTheme_CheckTheme(theme):
+    """Test loading all themes."""
+    themes = GuiTheme()
+    themes.iconCache = MagicMock()
+    themes._scanThemes(THEMES)
+
+    assert theme in themes.colourThemes
+    current = themes.colourThemes[theme]
+    if current.dark:
+        CONFIG.darkTheme = theme
+        CONFIG.themeMode = nwTheme.DARK
+    else:
+        CONFIG.lightTheme = theme
+        CONFIG.themeMode = nwTheme.LIGHT
+
+    # Check loading
+    themes.loadTheme()
+    assert themes._meta.name == current.name
+    assert themes.isDarkTheme == current.dark
+
+    # Check completeness
+    parser = ConfigParser()
+    parser.read(current.path, encoding="utf-8")
+
+    sections = ["Main", "Base", "Project", "Palette", "GUI", "Syntax"]
+    assert sorted(parser.sections()) == sorted(sections)
+
+    structure = {
+        "Main": [
+            "name", "mode",  # The rest are not required
+        ],
+        "Base": [
+            "default", "faded", "red", "orange", "yellow", "green", "cyan",
+            "blue", "purple",
+        ],
+        "Project": [
+            "root", "folder", "file", "title", "chapter", "scene", "note",
+        ],
+        "Palette": [
+            "window", "windowtext", "base", "alternatebase", "text",
+            "tooltipbase", "tooltiptext", "button", "buttontext", "brighttext",
+            "highlight", "highlightedtext", "link", "linkvisited",
+        ],
+        "GUI": [
+            "helptext", "fadedtext", "errortext",
+        ],
+        "Syntax": [
+            "background", "text", "link", "headertext", "headertag",
+            "emphasis", "dialog", "altdialog", "hidden", "note", "shortcode",
+            "keyword", "tag", "value", "optional", "spellcheckline",
+            "errorline", "replacetag", "modifier", "texthighlight",
+        ],
+    }
+    optional = ["description", "author", "credit", "url", "license", "licenseurl"]
+    missing = []
+    for section, options in structure.items():
+        missing.extend(opt for opt in options if opt not in parser[section])
+    assert missing == [], "Missing options in theme file"
+
+    # Check deprecated
+    deprecated = []
+    for section in sections:
+        deprecated.extend(
+            opt for opt in parser[section]
+            if opt not in structure[section] and opt not in optional
+        )
+    assert deprecated == [], "Deprecated options in theme file"
+
+
+ICONS = []
+_listContent(ICONS, CONFIG.assetPath("icons"), ".icons")
+
+
+@pytest.mark.gui
+@pytest.mark.parametrize("icons", [a.stem for a in ICONS])
+def testGuiTheme_CheckIcons(icons, tstPaths):
+    """Test loading all icons."""
+    keysFile: Path = tstPaths.filesDir / "all_icons.json"
+    iconKeys = json.loads(keysFile.read_text(encoding="utf-8"))
+    assert isinstance(iconKeys, list)
+
+    CONFIG.lightTheme = DEF_GUI_LIGHT
+    CONFIG.themeMode = nwTheme.LIGHT
+
+    themes = GuiTheme()
+    themes.initThemes()
+    iconCache = themes.iconCache
+
+    assert icons in iconCache.iconThemes
+    current = iconCache.iconThemes[icons]
+    CONFIG.iconTheme = icons
+
+    # Check loading
+    iconCache.loadTheme(icons)
+    assert iconCache._meta.name == current.name
+
+    # Check completeness
+    missing = [key for key in iconKeys if key not in iconCache._svgData]
+    assert missing == [], "Missing keys in icons file"
+
+    # Check deprecated
+    deprecated = [key for key in iconCache._svgData if key not in iconKeys]
+    assert deprecated == [], "Deprecated keys in icons file"
diff --git a/utils/icon_themes.py b/utils/icon_themes.py
index 752b29e5..acb2e230 100644
--- a/utils/icon_themes.py
+++ b/utils/icon_themes.py
@@ -33,6 +33,7 @@ from utils.common import ROOT_DIR
 UTILS = Path(__file__).parent
 ET.register_namespace("", "http://www.w3.org/2000/svg")
 ICONS = [
+    # Remember to also update tests/files/all_icons.json for test coverage
     "alert_error",
     "alert_info",
     "alert_question",