testing suite for dataframes (#379)

crates/nu-protocol/src/value/custom_value.rs

@@ -1,4 +1,4 @@
-use std::fmt;
+use std::{cmp::Ordering, fmt};
 
 use crate::{ast::Operator, Category, ShellError, Span, Value};
 
@@ -29,6 +29,9 @@ pub trait CustomValue: fmt::Debug + Send + Sync {
     fn follow_path_int(&self, count: usize, span: Span) -> Result<Value, ShellError>;
     fn follow_path_string(&self, column_name: String, span: Span) -> Result<Value, ShellError>;
 
+    // ordering with other value
+    fn partial_cmp(&self, other: &Value) -> Option<Ordering>;
+
     // Definition of an operation between the object that implements the trait
     // and another Value.
     // The Operator enum is used to indicate the expected operation

crates/nu-protocol/src/value/from.rs

@@ -1,5 +1,14 @@
 use crate::{ShellError, Span, Value};
 
+impl From<String> for Value {
+    fn from(val: String) -> Self {
+        Value::String {
+            val,
+            span: Span::unknown(),
+        }
+    }
+}
+
 impl From<bool> for Value {
     fn from(val: bool) -> Self {
         Value::Bool {

crates/nu-protocol/src/value/mod.rs

@@ -640,6 +640,7 @@ impl PartialOrd for Value {
             (Value::Binary { val: lhs, .. }, Value::Binary { val: rhs, .. }) => {
                 lhs.partial_cmp(rhs)
             }
+            (Value::CustomValue { val: lhs, .. }, rhs) => lhs.partial_cmp(rhs),
             (Value::Nothing { .. }, Value::Nothing { .. }) => Some(Ordering::Equal),
             (_, _) => None,
         }