Command tests (#922)

* WIP command tests

* Finish marking todo tests

* update

* update

* Windows cd test ignoring

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

@@ -0,0 +1,93 @@
+use nu_test_support::{nu, pipeline};
+
+const TEST_CWD: &str = "tests/fixtures/formats";
+
+// The To field in this email is just "to@example.com", which gets parsed out as the Address. The Name is empty.
+#[test]
+fn from_eml_get_to_field() {
+    let actual = nu!(
+        cwd: TEST_CWD,
+        pipeline(
+            r#"
+            open sample.eml
+            | get To
+            | get Address
+        "#
+        )
+    );
+
+    assert_eq!(actual.out, "to@example.com");
+
+    let actual = nu!(
+        cwd: TEST_CWD,
+        pipeline(
+            r#"
+            open sample.eml
+            | get To
+            | get Name
+        "#
+        )
+    );
+
+    assert_eq!(actual.out, "");
+}
+
+// The Reply-To field in this email is "replyto@example.com" <replyto@example.com>, meaning both the Name and Address values are identical.
+#[test]
+fn from_eml_get_replyto_field() {
+    let actual = nu!(
+        cwd: TEST_CWD,
+        pipeline(
+            r#"
+            open sample.eml
+            | get Reply-To
+            | get Address
+        "#
+        )
+    );
+
+    assert_eq!(actual.out, "replyto@example.com");
+
+    let actual = nu!(
+        cwd: TEST_CWD,
+        pipeline(
+            r#"
+            open sample.eml
+            | get Reply-To
+            | get Name
+        "#
+        )
+    );
+
+    assert_eq!(actual.out, "replyto@example.com");
+}
+
+#[test]
+fn from_eml_get_subject_field() {
+    let actual = nu!(
+        cwd: TEST_CWD,
+        pipeline(
+            r#"
+            open sample.eml
+            | get Subject
+        "#
+        )
+    );
+
+    assert_eq!(actual.out, "Test Message");
+}
+
+#[test]
+fn from_eml_get_another_header_field() {
+    let actual = nu!(
+        cwd: TEST_CWD,
+        pipeline(
+            r#"
+            open sample.eml
+            | get MIME-Version
+        "#
+        )
+    );
+
+    assert_eq!(actual.out, "1.0");
+}