Example showing discovery and running of test commands

Author: vyadh

book/testing.md

@@ -165,4 +165,63 @@ for t in [
 ```
 and be invoked as `nu tests.nu`
 
+### Basic Test Framework
+
+It is also possible to define tests in Nushell as functions with descriptive names and discover
+them dynamically without requiring a [Nupm] package. The following uses `scope commands` and a
+second instance of Nushell to run the generated list of tests.
+
+```nushell
+use std assert
+
+source fib.nu
+
+def main [] {
+  print "Running tests..."
+
+  let test_commands = (
+    scope commands
+      # Exclude all in-built commands
+      | where ($it.type == "custom")
+      # Include all commands starting with "test_"
+      | where ($it.name | str starts-with "test_")
+      # Exclude commands marked as "ignored" in the description
+      | where not ($it.description | str starts-with "ignore")
+      # Get the name of the test command
+      | get name
+      # Prefix each test command with a command to print the test name
+      | each { |test| [$"print 'Running test: ($test)'", $test] } | flatten
+      # Concatenate into a command list
+      | str join "; "
+  )
+
+  nu --commands $"source ($env.CURRENT_FILE); ($tests)"
+  print "Tests completed successfully"
+}
+
+def test_fib [] {
+  for t in [
+      [input, expected];
+      [0, 0],
+      [1, 1],
+      [2, 1],
+      [3, 2],
+      [4, 3],
+      [5, 5],
+      [6, 8],
+      [7, 13]
+  ] {
+    assert equal (fib $t.input) $t.expected
+  }
+}
+
+# ignore
+def test_fib_ignored_test [] {
+  print "This test will not be executed"
+}
+```
+
+This is a simple example but could be extended to include many of the things you might expect from
+a testing framework, including setup and tear down functions and test discovery across files.
+
 [Nupm]: https://github.com/nushell/nupm