Fixes MDAnalysis.analysis.density.convert_density() method has an invalid default unit value

package/CHANGELOG

@@ -19,6 +19,7 @@ The rules for this file:
  * 2.9.0
 
 Fixes
+ * Fixes invalid default unit from Angstrom to Angstrom^{-3} for convert_density() function. (Issue #4829)
  * Fixes deprecation warning Array to scalar convertion. Replaced atan2() with np.arctan2() (Issue #4339)
  * Replaced mutable defaults with None and initialized them within
    the function to prevent shared state. (Issue #4655)

package/MDAnalysis/analysis/density.py

@@ -826,7 +826,7 @@ def convert_length(self, unit='Angstrom'):
         self.units['length'] = unit
         self._update()  # needed to recalculate midpoints and origin
 
-    def convert_density(self, unit='Angstrom'):
+    def convert_density(self, unit='Angstrom^{-3}'):
         """Convert the density to the physical units given by `unit`.
 
         Parameters

testsuite/MDAnalysisTests/analysis/test_density.py

@@ -384,6 +384,12 @@ def test_warn_results_deprecated(self, universe):
         with pytest.warns(DeprecationWarning, match=wmsg):
             assert_equal(D.density.grid, D.results.density.grid)
 
+    def test_density_analysis_conversion_default_unit(self):
+        u = mda.Universe(TPR, XTC)
+        ow = u.select_atoms("name OW")
+        D = mda.analysis.density.DensityAnalysis(ow, delta=1.0)
+        D.run()
+        D.results.density.convert_density()
 
 class TestGridImport(object):