Refactor command-line handling into modules per subcommands

cli/tests/cli.rs

@@ -0,0 +1,42 @@
+use assert_cmd::prelude::*;
+use predicates::prelude::*;
+use std::process::Command;
+
+// This tests that the task binary is running and parsing arguments.  The details of subcommands
+// are handled with unit tests.
+
+#[test]
+fn help() -> Result<(), Box<dyn std::error::Error>> {
+    let mut cmd = Command::cargo_bin("task")?;
+
+    cmd.arg("--help");
+    cmd.assert()
+        .success()
+        .stdout(predicate::str::contains("Personal task-tracking"));
+
+    Ok(())
+}
+
+#[test]
+fn version() -> Result<(), Box<dyn std::error::Error>> {
+    let mut cmd = Command::cargo_bin("task")?;
+
+    cmd.arg("--version");
+    cmd.assert()
+        .success()
+        .stdout(predicate::str::contains("TaskChampion"));
+
+    Ok(())
+}
+
+#[test]
+fn invalid_option() -> Result<(), Box<dyn std::error::Error>> {
+    let mut cmd = Command::cargo_bin("task")?;
+
+    cmd.arg("--no-such-option");
+    cmd.assert()
+        .failure()
+        .stderr(predicate::str::contains("USAGE"));
+
+    Ok(())
+}