I need help writing a Python function to convert weights of common ingredients like flour, yeast, salt, oil, sugar, etc to fractional volume measurements typically used in recipes.

The supported volume units should include:

• 1 cup, 1/2 cup, 1/3 cup, 1/4 cup
• 1 tablespoon
• 1 teaspoon, 1/2 teaspoon, 1/4 teaspoon

The function should be able to handle input weights in at least grams, and it would be better if it could handle input weights in grams, ounces and pounds.

Here are some test cases:

def test_function():
    assert func(1.5, 'lb', 'flour') == '5 3/4 cup'
    assert func(150, 'g', 'flour') == '1 1/4 cup' 
    assert func(42, 'g', 'sugar') == '3 tablespoon'
    assert func(5, 'oz', 'salt') == '3 tablespoon'
    assert func(7.1125, 'g', 'salt') == '1 1/4 teaspoon'

How could I write this conversion function to handle the fractional volume measurements?