Command tests (#922)

* WIP command tests

* Finish marking todo tests

* update

* update

* Windows cd test ignoring

crates/nu-command/tests/format_conversions/markdown.rs

@@ -0,0 +1,98 @@
+use nu_test_support::{nu, pipeline};
+
+#[test]
+fn md_empty() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+            echo [[]; []] | from json | to md
+        "#
+    ));
+
+    assert_eq!(actual.out, "");
+}
+
+#[test]
+fn md_empty_pretty() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+            echo "{}" | from json | to md -p
+        "#
+    ));
+
+    assert_eq!(actual.out, "");
+}
+
+#[test]
+fn md_simple() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+            echo 3 | to md
+        "#
+    ));
+
+    assert_eq!(actual.out, "3");
+}
+
+#[test]
+fn md_simple_pretty() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+            echo 3 | to md -p
+        "#
+    ));
+
+    assert_eq!(actual.out, "3");
+}
+
+#[test]
+fn md_table() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+            echo [[name]; [jason]] | to md
+        "#
+    ));
+
+    assert_eq!(actual.out, "|name||-||jason|");
+}
+
+#[test]
+fn md_table_pretty() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+            echo [[name]; [joseph]] | to md -p
+        "#
+    ));
+
+    assert_eq!(actual.out, "| name   || ------ || joseph |");
+}
+
+#[test]
+fn md_combined() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+            def title [] {
+                echo [[H1]; ["Nu top meals"]]
+            };
+
+            def meals [] {
+                echo [[dish]; [Arepa] [Taco] [Pizza]]
+            };
+
+            title
+            | append (meals)
+            | to md --per-element --pretty
+        "#
+    ));
+
+    assert_eq!(
+        actual.out,
+        "# Nu top meals| dish  || ----- || Arepa || Taco  || Pizza |"
+    );
+}