Add insert and update back (#4864)

crates/nu-command/tests/commands/insert.rs

@@ -0,0 +1,28 @@
+use nu_test_support::{nu, pipeline};
+
+#[test]
+fn insert_the_column() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            open cargo_sample.toml
+            | insert dev-dependencies.new_assertions "0.7.0"
+            | get dev-dependencies.new_assertions
+        "#
+    ));
+
+    assert_eq!(actual.out, "0.7.0");
+}
+
+#[test]
+fn insert_the_column_conflict() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            open cargo_sample.toml
+            | insert dev-dependencies.pretty_assertions "0.7.0"
+        "#
+    ));
+
+    assert!(actual.err.contains("column already exists"));
+}