diff --git a/tests/hghave.py b/tests/hghave.py
--- a/tests/hghave.py
+++ b/tests/hghave.py
@@ -188,6 +188,11 @@ def has_chg():
     return 'CHGHG' in os.environ
 
 
+@check("rhg", "running with rhg as 'hg'")
+def has_rhg():
+    return 'RHG_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
@@ -3134,6 +3134,8 @@ class TestRunner(object):
         # configure fallback and replace "hg" command by "rhg"
         rhgbindir = self._bindir
         if self.options.rhg or self.options.with_rhg:
+            # Affects hghave.py
+            osenvironb[b'RHG_INSTALLED_AS_HG'] = b'1'
             # Affects configuration. Alternatives would be setting configuration through
             # `$HGRCPATH` but some tests override that, or changing `_hgcommand` to include
             # `--config` but that disrupts tests that print command lines and check expected
diff --git a/tests/test-rhg.t b/tests/test-rhg.t
--- a/tests/test-rhg.t
+++ b/tests/test-rhg.t
@@ -1,15 +1,4 @@
-#require rust
-
-Define an rhg function that will only run if rhg exists
-  $ RHG="$RUNTESTDIR/../rust/target/release/rhg"
-  $ rhg() {
-  > if [ -f "$RHG" ]; then
-  >   "$RHG" "$@"
-  > else
-  >   echo "skipped: Cannot find rhg. Try to run cargo build in rust/rhg."
-  >   exit 80
-  > fi
-  > }
+#require rhg
 
   $ NO_FALLBACK="env RHG_ON_UNSUPPORTED=abort"
 
@@ -169,8 +158,8 @@ Fallback to Python
   unsupported feature: `rhg cat` without `--rev` / `-r`
   [252]
 
-  $ rhg cat original --config rhg.fallback-executable="$RHG"
-  Blocking recursive fallback. The 'rhg.fallback-executable = */rust/target/release/rhg' config points to `rhg` itself. (glob)
+  $ rhg cat original --config rhg.fallback-executable=rhg
+  Blocking recursive fallback. The 'rhg.fallback-executable = rhg' config points to `rhg` itself.
   unsupported feature: `rhg cat` without `--rev` / `-r`
   [252]