You should be able use the String value in the Attribute and set the Parameter type to Decimal, it get’s converted automatically by the Test Framework as far as I can tell.
[Theory]
[InlineData("37.60")]
public void MyDecimalTest(Decimal number)
{
Assert.Equal(number, 37.60M);
}
If this doesn’t work then you can manually convert it by passing in a String parameter.
[Theory]
[InlineData("37.60")]
public void MyDecimalTest(String number)
{
var d = Convert.ToDecimal(number);
Assert.Equal(d, 37.60M);
}