Command tests (#922)

* WIP command tests

* Finish marking todo tests

* update

* update

* Windows cd test ignoring

crates/nu-command/tests/commands/math/sqrt.rs

@@ -0,0 +1,35 @@
+use nu_test_support::nu;
+
+// FIXME: jt: needs more work
+#[ignore]
+#[test]
+fn can_sqrt_numbers() {
+    let actual = nu!(
+        cwd: ".",
+        "echo [0.25 2 4] | math sqrt | math sum"
+    );
+
+    assert_eq!(actual.out, "3.914213562373095048801688724209698078569671875376948073176679737990732478462107038850387534327641573");
+}
+
+// FIXME: jt: needs more work
+#[ignore]
+#[test]
+fn can_sqrt_irrational() {
+    let actual = nu!(
+        cwd: ".",
+        "echo 2 | math sqrt"
+    );
+
+    assert_eq!(actual.out, "1.414213562373095048801688724209698078569671875376948073176679737990732478462107038850387534327641573");
+}
+
+#[test]
+fn can_sqrt_perfect_square() {
+    let actual = nu!(
+        cwd: ".",
+        "echo 4 | math sqrt"
+    );
+
+    assert_eq!(actual.out, "2");
+}