diff --git a/spec/highlight_groups_spec.lua b/spec/highlight_groups_spec.lua
deleted file mode 100644
index 23c79ee..0000000
--- a/spec/highlight_groups_spec.lua
+++ /dev/null
@@ -1,55 +0,0 @@
-require('spec.helpers')
-local config = require('diffs.config')
-local highlight_groups = require('diffs.runtime.highlight_groups')
-local stub = require('luassert.stub')
-
-describe('conflict highlight groups', function()
-  local source
-  local groups
-
-  before_each(function()
-    source = {
-      Normal = { fg = 0xe4e4ef, bg = 0x181818 },
-      DiffAdd = { bg = 0x1a3a1a },
-      diffAdded = { fg = 0x80d080 },
-      diffRemoved = { fg = 0xd08080 },
-      DiffChange = { fg = 0x80a0c0, bg = 0x565f73 },
-      DiffText = { bg = 0x52494e },
-    }
-    groups = {}
-    stub(vim.api, 'nvim_get_hl', function(_, opts)
-      return source[opts.name] or {}
-    end)
-    stub(vim.api, 'nvim_set_hl', function(_, name, attrs)
-      groups[name] = attrs
-    end)
-  end)
-
-  after_each(function()
-    vim.api.nvim_get_hl:revert()
-    vim.api.nvim_set_hl:revert()
-  end)
-
-  it('uses the DiffText foreground for base line numbers', function()
-    source.DiffText.fg = 0xe0a080
-
-    highlight_groups.apply(config.new())
-
-    assert.are.equal(source.DiffText.fg, groups.DiffsConflictBaseNr.fg)
-    assert.are.equal(source.DiffChange.fg, groups.DiffsConflictTheirsNr.fg)
-    assert.are.equal(source.diffAdded.fg, groups.DiffsConflictOursNr.fg)
-    assert.are.equal(groups.DiffsConflictBase.bg, groups.DiffsConflictBaseNr.bg)
-  end)
-
-  it('falls back to the deletion foreground for background-only diff groups', function()
-    source.DiffChange.fg = nil
-
-    highlight_groups.apply(config.new())
-
-    assert.are.equal(source.diffRemoved.fg, groups.DiffsConflictBaseNr.fg)
-    assert.are.equal(0x80a0c0, groups.DiffsConflictTheirsNr.fg)
-    assert.are.equal(source.diffAdded.fg, groups.DiffsConflictOursNr.fg)
-    assert.are.equal(0x353033, groups.DiffsConflictBase.bg)
-    assert.are.equal(groups.DiffsConflictBase.bg, groups.DiffsConflictBaseNr.bg)
-  end)
-end)
diff --git a/spec/runtime_spec.lua b/spec/runtime_spec.lua
index 0acd46c..1c02d10 100644
--- a/spec/runtime_spec.lua
+++ b/spec/runtime_spec.lua
@@ -411,6 +411,21 @@ describe('diffs.runtime', function()
       assert.is_number(set_calls.DiffsDeleteBar.bg)
     end)
 
+    it('uses deletion colors for base numbers on background-only themes', function()
+      local source = {
+        DiffChange = { bg = 0x565f73 },
+        DiffText = { bg = 0x52494e },
+        diffRemoved = { fg = 0xd08080 },
+      }
+      vim.api.nvim_get_hl = function(ns, opts)
+        return source[opts.name] or saved_get_hl(ns, opts)
+      end
+      runtime._test.compute_highlight_groups()
+      assert.are.equal(0xd08080, set_calls.DiffsConflictBaseNr.fg)
+      assert.are.equal(0x80a0c0, set_calls.DiffsConflictTheirsNr.fg)
+      assert.are.equal(set_calls.DiffsConflictBase.bg, set_calls.DiffsConflictBaseNr.bg)
+    end)
+
     it('blend_alpha controls DiffsAdd.bg intensity', function()
       local saved_config_alpha = runtime._test.get_config().highlights.blend_alpha
       runtime._test.get_config().highlights.blend_alpha = 0.3