Minor Math Sum Additions (#2007)

* Move sum tests into math directory

* Move sum documentation over to math documentation

One sum example already existed in the math examples and a few of the others were outdated and didn't work, so I only moved one over, and updated their output

* Remove no-longer-in-use mod statement

crates/nu-cli/tests/commands/math/sum.rs

@@ -0,0 +1,116 @@
+use nu_test_support::fs::Stub::FileWithContentToBeTrimmed;
+use nu_test_support::playground::Playground;
+use nu_test_support::{nu, pipeline};
+use std::str::FromStr;
+
+#[test]
+fn all() {
+    Playground::setup("sum_test_1", |dirs, sandbox| {
+        sandbox.with_files(vec![FileWithContentToBeTrimmed(
+            "meals.json",
+            r#"
+                {
+                    meals: [
+                        {description: "1 large egg", calories: 90},
+                        {description: "1 cup white rice", calories: 250},
+                        {description: "1 tablespoon fish oil", calories: 108}
+                    ]
+                }
+            "#,
+        )]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                open meals.json
+                | get meals
+                | get calories
+                | math sum
+                | echo $it
+            "#
+        ));
+
+        assert_eq!(actual.out, "448");
+    })
+}
+
+#[test]
+fn outputs_zero_with_no_input() {
+    Playground::setup("sum_test_2", |dirs, sandbox| {
+        sandbox.with_files(vec![FileWithContentToBeTrimmed(
+            "meals.json",
+            r#"
+                {
+                    meals: [
+                        {description: "1 large egg", calories: 90},
+                        {description: "1 cup white rice", calories: 250},
+                        {description: "1 tablespoon fish oil", calories: 108}
+                    ]
+                }
+            "#,
+        )]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                math sum
+                | echo $it
+            "#
+        ));
+
+        assert_eq!(actual.out, "0");
+    })
+}
+
+#[test]
+#[allow(clippy::unreadable_literal)]
+#[allow(clippy::float_cmp)]
+fn compute_sum_of_individual_row() -> Result<(), String> {
+    let answers_for_columns = [
+        ("cpu", 88.257434),
+        ("mem", 3032375296.),
+        ("virtual", 102579965952.),
+    ];
+    for (column_name, expected_value) in answers_for_columns.iter() {
+        let actual = nu!(
+            cwd: "tests/fixtures/formats/",
+            format!("open sample-ps-output.json | select {} | math sum | get {}", column_name, column_name)
+        );
+        let result =
+            f64::from_str(&actual.out).map_err(|_| String::from("Failed to parse float."))?;
+        assert_eq!(result, *expected_value);
+    }
+    Ok(())
+}
+
+#[test]
+#[allow(clippy::unreadable_literal)]
+#[allow(clippy::float_cmp)]
+fn compute_sum_of_table() -> Result<(), String> {
+    let answers_for_columns = [
+        ("cpu", 88.257434),
+        ("mem", 3032375296.),
+        ("virtual", 102579965952.),
+    ];
+    for (column_name, expected_value) in answers_for_columns.iter() {
+        let actual = nu!(
+            cwd: "tests/fixtures/formats/",
+            format!("open sample-ps-output.json | select cpu mem virtual | math sum | get {}", column_name)
+        );
+        let result =
+            f64::from_str(&actual.out).map_err(|_| String::from("Failed to parse float."))?;
+        assert_eq!(result, *expected_value);
+    }
+    Ok(())
+}
+
+#[test]
+fn sum_of_a_row_containing_a_table_is_an_error() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats/",
+        "open sample-sys-output.json | math sum"
+    );
+    assert!(actual
+        .err
+        .contains("Attempted to compute the sum of a value that cannot be summed."));
+}