units: fixed convert_to() bug and added some tests

.mailmap

@@ -799,6 +799,7 @@ Joseph Rance <56409230+Joseph-Rance@users.noreply.github.com>
 Joseph Redfern <joseph@redfern.me>
 Josh Burkart <jburkart@gmail.com>
 José Senart <jose.senart@gmail.com>
+João Bravo <joaocgbravo@tecnico.ulisboa.pt>
 João Moura <operte@gmail.com>
 Juan Barbosa <js.barbosa10@uniandes.edu.co>
 Juan Felipe Osorio <jfosorio@gmail.com>

sympy/physics/units/tests/test_util.py

@@ -76,6 +76,10 @@ def test_convert_to_quantities():
 
 
 def test_convert_to_tuples_of_quantities():
+    from sympy.core.symbol import symbols
+
+    alpha, beta = symbols('alpha beta')
+
     assert convert_to(speed_of_light, [meter, second]) == 299792458 * meter / second
     assert convert_to(speed_of_light, (meter, second)) == 299792458 * meter / second
     assert convert_to(speed_of_light, Tuple(meter, second)) == 299792458 * meter / second
@@ -98,6 +102,9 @@ def test_convert_to_tuples_of_quantities():
     assert convert_to(sqrt(meter**2 + second**2.0), [meter, second]) == sqrt(meter**2 + second**2.0)
     assert convert_to((meter**2 + second**2.0)**2, [meter, second]) == (meter**2 + second**2.0)**2
 
+    # similar to https://github.com/sympy/sympy/issues/21463
+    assert convert_to(1/(beta*meter + meter), 1/meter) == 1/(beta*meter + meter)
+    assert convert_to(1/(beta*meter + alpha*meter), 1/kilometer) == (1/(kilometer*beta/1000 + alpha*kilometer/1000))
 
 def test_eval_simplify():
     from sympy.physics.units import cm, mm, km, m, K, kilo

sympy/physics/units/util.py

@@ -12,6 +12,7 @@
 from sympy.core.power import Pow
 from sympy.core.sorting import ordered
 from sympy.core.sympify import sympify
+from sympy.core.function import Function
 from sympy.matrices.exceptions import NonInvertibleMatrixError
 from sympy.physics.units.dimensions import Dimension, DimensionSystem
 from sympy.physics.units.prefixes import Prefix
@@ -110,6 +111,9 @@ def handle_Adds(expr):
     expr = sympify(expr)
     target_units = sympify(target_units)
 
+    if isinstance(expr, Function):
+        expr = expr.together()
+
     if not isinstance(expr, Quantity) and expr.has(Quantity):
         expr = expr.replace(lambda x: isinstance(x, Quantity),
             lambda x: x.convert_to(target_units, unit_system))