Add example tests (nu-plugin-test-support) for plugins in repo (#12281)

# Description

Uses the new `nu-plugin-test-support` crate to test the examples of
commands provided by plugins in the repo.

Also fixed some of the examples to pass.

# User-Facing Changes

- Examples that are more guaranteed to work

# Tests + Formatting
- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

crates/nu_plugin_example/src/commands/collect_external.rs

@@ -51,3 +51,9 @@ impl PluginCommand for CollectExternal {
         })
     }
 }
+
+#[test]
+fn test_examples() -> Result<(), nu_protocol::ShellError> {
+    use nu_plugin_test_support::PluginTest;
+    PluginTest::new("example", Example.into())?.test_command_examples(&CollectExternal)
+}

crates/nu_plugin_example/src/commands/for_each.rs

@@ -45,3 +45,9 @@ impl PluginCommand for ForEach {
         Ok(PipelineData::Empty)
     }
 }
+
+#[test]
+fn test_examples() -> Result<(), nu_protocol::ShellError> {
+    use nu_plugin_test_support::PluginTest;
+    PluginTest::new("example", Example.into())?.test_command_examples(&ForEach)
+}

crates/nu_plugin_example/src/commands/generate.rs

@@ -76,3 +76,12 @@ impl PluginCommand for Generate {
         .into_pipeline_data(None))
     }
 }
+
+#[test]
+fn test_examples() -> Result<(), nu_protocol::ShellError> {
+    use nu_cmd_lang::If;
+    use nu_plugin_test_support::PluginTest;
+    PluginTest::new("example", Example.into())?
+        .add_decl(Box::new(If))?
+        .test_command_examples(&Generate)
+}

crates/nu_plugin_example/src/commands/one.rs

@@ -41,3 +41,9 @@ impl SimplePluginCommand for One {
         Ok(Value::nothing(call.head))
     }
 }
+
+#[test]
+fn test_examples() -> Result<(), nu_protocol::ShellError> {
+    use nu_plugin_test_support::PluginTest;
+    PluginTest::new("example", Example.into())?.test_command_examples(&One)
+}

crates/nu_plugin_example/src/commands/seq.rs

@@ -46,3 +46,9 @@ impl PluginCommand for Seq {
         Ok(PipelineData::ListStream(list_stream, None))
     }
 }
+
+#[test]
+fn test_examples() -> Result<(), nu_protocol::ShellError> {
+    use nu_plugin_test_support::PluginTest;
+    PluginTest::new("example", Example.into())?.test_command_examples(&Seq)
+}

crates/nu_plugin_example/src/commands/sum.rs

@@ -20,7 +20,7 @@ impl PluginCommand for Sum {
                 (Type::List(Type::Float.into()), Type::Float),
             ])
             .plugin_examples(vec![PluginExample {
-                example: "seq 1 5 | example sum".into(),
+                example: "example seq 1 5 | example sum".into(),
                 description: "sum values from 1 to 5".into(),
                 result: Some(Value::test_int(15)),
             }])
@@ -88,3 +88,9 @@ impl IntOrFloat {
         }
     }
 }
+
+#[test]
+fn test_examples() -> Result<(), nu_protocol::ShellError> {
+    use nu_plugin_test_support::PluginTest;
+    PluginTest::new("example", Example.into())?.test_command_examples(&Sum)
+}