diff --git a/tests/hghave.py b/tests/hghave.py
--- a/tests/hghave.py
+++ b/tests/hghave.py
@@ -199,6 +199,11 @@
     return 'RHG_INSTALLED_AS_HG' in os.environ
 
 
+@check("pyoxidizer", "running with pyoxidizer build as 'hg'")
+def has_rhg():
+    return 'PYOXIDIZED_INSTALLED_AS_HG' in os.environ
+
+
 @check("cvs", "cvs client/server")
 def has_cvs():
     re = br'Concurrent Versions System.*?server'
diff --git a/tests/run-tests.py b/tests/run-tests.py
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -3241,6 +3241,10 @@
             )
             full_path = os.path.join(reporootdir, bin_path)
             self._hgcommand = full_path
+            # Affects hghave.py
+            osenvironb[b'PYOXIDIZED_INSTALLED_AS_HG'] = b'1'
+        else:
+            osenvironb.pop(b'PYOXIDIZED_INSTALLED_AS_HG', None)
 
         osenvironb[b"BINDIR"] = self._bindir
         osenvironb[b"PYTHON"] = PYTHON