FIX: Several fixes on the FV function

(1+x)^(1+y) was stringifyfied incorrectly
We still need work on this

FV now returns currency

FV(-1,-2,1) should return #DIV/0! not #NUM!

base/src/expressions/parser/tests/test_stringify.rs

@@ -0,0 +1,34 @@
+#![allow(clippy::panic)]
+
+use std::collections::HashMap;
+
+use crate::expressions::parser::stringify::to_string;
+use crate::expressions::parser::Parser;
+use crate::expressions::types::CellReferenceRC;
+
+#[test]
+fn exp_order() {
+    let worksheets = vec!["Sheet1".to_string()];
+    let mut parser = Parser::new(worksheets, HashMap::new());
+
+    // Reference cell is Sheet1!A1
+    let cell_reference = CellReferenceRC {
+        sheet: "Sheet1".to_string(),
+        row: 1,
+        column: 1,
+    };
+    let t = parser.parse("(1 + 2)^3  + 4", &Some(cell_reference.clone()));
+    assert_eq!(to_string(&t, &cell_reference), "(1+2)^3+4");
+
+    let t = parser.parse("(C5 + 3)^R4", &Some(cell_reference.clone()));
+    assert_eq!(to_string(&t, &cell_reference), "(C5+3)^R4");
+
+    let t = parser.parse("(C5 + 3)^(R4*6)", &Some(cell_reference.clone()));
+    assert_eq!(to_string(&t, &cell_reference), "(C5+3)^(R4*6)");
+
+    let t = parser.parse("(C5)^(R4)", &Some(cell_reference.clone()));
+    assert_eq!(to_string(&t, &cell_reference), "C5^R4");
+
+    let t = parser.parse("(5)^(4)", &Some(cell_reference.clone()));
+    assert_eq!(to_string(&t, &cell_reference), "5^4");
+}