Default TestContext::command() working directory to temp_dir

Tests were flaky because command() inherited the real repo as the
working directory. When the repo was clean, detached runs attempted
git worktree creation against it, sometimes failing and injecting
extra warning lines into snapshots.

Now command() defaults to the non-git temp_dir, eliminating this
class of flakiness. Tests needing a specific directory override with
.current_dir(). Also canonicalizes fixture paths and adds a
[FIXTURES] snapshot filter via test_context!() macro.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/crates/fabro-cli/tests/it/cmd/attach.rs

@@ -103,7 +103,6 @@ fn attach_before_completion_streams_to_finished_state() {
     let gate = write_gated_workflow(&context.temp_dir.join("slow.fabro"), "slow", "Run slowly");
 
     let mut run_cmd = context.command();
-    run_cmd.current_dir(&context.temp_dir);
     run_cmd.env("OPENAI_API_KEY", "test");
     run_cmd.args([
         "run",
@@ -136,7 +135,6 @@ fn attach_before_completion_streams_to_finished_state() {
         gate.release();
     });
     let mut attach_cmd = context.command();
-    attach_cmd.current_dir(&context.temp_dir);
     attach_cmd.args(["attach", &run_id]);
     let (snapshot, _output) = run_and_format(&mut attach_cmd, &filters);
     release_gate.join().expect("gate releaser should join");
@@ -176,7 +174,6 @@ fn attach_json_errors_without_prompting_for_human_input() {
 
     let run_output = context
         .command()
-        .current_dir(&context.temp_dir)
         .env("OPENAI_API_KEY", "test")
         .args([
             "run",

lib/crates/fabro-cli/tests/it/cmd/detached.rs

@@ -187,7 +187,6 @@ digraph Test {
 
     let run = context
         .command()
-        .current_dir(&context.temp_dir)
         .args([
             "run",
             "--dry-run",

lib/crates/fabro-cli/tests/it/cmd/exec.rs

@@ -75,7 +75,6 @@ fn exec_missing_api_key_exits_with_error() {
     cmd.arg("test prompt");
     cmd.env_clear();
     cmd.env("HOME", &context.home_dir);
-    cmd.current_dir(&context.temp_dir);
     fabro_snapshot!(context.filters(), cmd, @"
     success: false
     exit_code: 1
@@ -99,7 +98,6 @@ fn exec_uses_user_config_defaults() {
     cmd.env("HOME", &context.home_dir);
     cmd.env("FABRO_STORAGE_DIR", &context.storage_dir);
     cmd.env("FABRO_NO_UPGRADE_CHECK", "true");
-    cmd.current_dir(&context.temp_dir);
 
     fabro_snapshot!(context.filters(), cmd, @"
     success: false
@@ -125,7 +123,6 @@ fn exec_creates_file() {
             "claude-haiku-4-5",
             "Create a file called hello.txt containing exactly 'Hello'",
         ])
-        .current_dir(&context.temp_dir)
         .timeout(std::time::Duration::from_secs(120))
         .assert()
         .success();
@@ -153,7 +150,6 @@ fn exec_shell_command() {
             "claude-haiku-4-5",
             "Run the shell command `echo arc_test_marker_42` and tell me what it printed",
         ])
-        .current_dir(&context.temp_dir)
         .timeout(std::time::Duration::from_secs(120))
         .assert()
         .success();
@@ -174,7 +170,6 @@ fn exec_read_only_blocks_write() {
             "claude-haiku-4-5",
             "Create a file called forbidden.txt containing 'should not exist'",
         ])
-        .current_dir(&context.temp_dir)
         .timeout(std::time::Duration::from_secs(120))
         .assert()
         .success();
@@ -201,7 +196,6 @@ fn exec_json_output_format() {
             "claude-haiku-4-5",
             "Create a file called test.txt containing 'test'",
         ])
-        .current_dir(&context.temp_dir)
         .timeout(std::time::Duration::from_secs(120))
         .assert()
         .success()
@@ -237,7 +231,6 @@ fn exec_read_and_edit() {
             "claude-haiku-4-5",
             "Read data.txt then replace its entire content with 'new content'",
         ])
-        .current_dir(&context.temp_dir)
         .timeout(std::time::Duration::from_secs(120))
         .assert()
         .success();

lib/crates/fabro-cli/tests/it/cmd/fork.rs

@@ -42,7 +42,6 @@ fn help() {
 fn fork_outside_git_repo_errors() {
     let context = test_context!();
     let mut cmd = context.command();
-    cmd.current_dir(&context.temp_dir);
     cmd.args(["fork", "01ARZ3NDEKTSV4RRFFQ69G5FAW"]);
 
     fabro_snapshot!(context.filters(), cmd, @"

lib/crates/fabro-cli/tests/it/cmd/parse.rs

@@ -36,7 +36,6 @@ fn parse_valid_workflow_prints_ast_json() {
         "digraph Tiny {\n  graph [goal=\"Parse a tiny workflow\"]\n  start [shape=Mdiamond]\n  exit [shape=Msquare]\n  main [label=\"Main\", prompt=\"Do the thing\"]\n  start -> main -> exit\n}\n",
     );
     let mut cmd = context.command();
-    cmd.current_dir(&context.temp_dir);
     cmd.args(["parse", "tiny.fabro"]);
 
     fabro_snapshot!(context.filters(), cmd, @r###"
@@ -125,7 +124,6 @@ fn parse_invalid_dot_fails_cleanly() {
         "digraph Bad {\n  start [shape=Mdiamond]\n  exit [shape=Msquare]\n  start -> exit\n",
     );
     let mut cmd = context.command();
-    cmd.current_dir(&context.temp_dir);
     cmd.args(["parse", "bad.fabro"]);
 
     fabro_snapshot!(context.filters(), cmd, @"

lib/crates/fabro-cli/tests/it/cmd/preflight.rs

@@ -49,7 +49,7 @@ fn preflight_invalid_workflow_fails_with_validation_output() {
     ----- stdout -----
     ----- stderr -----
     Workflow: Invalid (2 nodes, 1 edges)
-    Graph: ../../../test/invalid.fabro
+    Graph: [FIXTURES]/invalid.fabro
     error: Pipeline must have exactly one start node (shape=Mdiamond or id start/Start) (start_node)
     error [node: exit]: Exit node 'exit' has 1 outgoing edge(s) but must have none (exit_no_outgoing)
     error: Validation failed

lib/crates/fabro-cli/tests/it/cmd/repo.rs

@@ -46,12 +46,7 @@ fn test_repo_deinit_removes_fabro_toml_and_dir() {
     assert!(context.temp_dir.join("fabro.toml").exists());
     assert!(context.temp_dir.join("fabro").exists());
 
-    context
-        .repo()
-        .arg("deinit")
-        .current_dir(&context.temp_dir)
-        .assert()
-        .success();
+    context.repo().arg("deinit").assert().success();
 
     assert!(
         !context.temp_dir.join("fabro.toml").exists(),
@@ -70,7 +65,6 @@ fn test_repo_deinit_fails_when_not_initialized() {
 
     let mut cmd = context.repo();
     cmd.arg("deinit");
-    cmd.current_dir(&context.temp_dir);
     fabro_snapshot!(context.filters(), cmd, @"
     success: false
     exit_code: 1
@@ -85,12 +79,7 @@ fn test_repo_init_skill_installs_skill_files() {
     let context = test_context!();
     context.git_init();
 
-    context
-        .repo()
-        .args(["init", "--skill"])
-        .current_dir(&context.temp_dir)
-        .assert()
-        .success();
+    context.repo().args(["init", "--skill"]).assert().success();
 
     // Skill files should be installed under .claude/skills/fabro-create-workflow/
     let skill_dir = context

lib/crates/fabro-cli/tests/it/cmd/repo_init.rs

@@ -33,7 +33,6 @@ fn repo_init_creates_fabro_toml_and_hello_workflow() {
     context.git_init();
 
     let mut cmd = context.command();
-    cmd.current_dir(&context.temp_dir);
     cmd.args(["repo", "init"]);
 
     fabro_snapshot!(context.filters(), cmd, @"
@@ -111,7 +110,6 @@ fn repo_init_rejects_already_initialized_repo() {
     std::fs::write(context.temp_dir.join("fabro.toml"), "version = 1\n").unwrap();
 
     let mut cmd = context.command();
-    cmd.current_dir(&context.temp_dir);
     cmd.args(["repo", "init"]);
 
     fabro_snapshot!(context.filters(), cmd, @"
@@ -127,7 +125,6 @@ fn repo_init_rejects_already_initialized_repo() {
 fn repo_init_errors_outside_git_repo() {
     let context = test_context!();
     let mut cmd = context.command();
-    cmd.current_dir(&context.temp_dir);
     cmd.args(["repo", "init"]);
 
     fabro_snapshot!(context.filters(), cmd, @"

lib/crates/fabro-cli/tests/it/cmd/rewind.rs

@@ -42,7 +42,6 @@ fn help() {
 fn rewind_outside_git_repo_errors() {
     let context = test_context!();
     let mut cmd = context.command();
-    cmd.current_dir(&context.temp_dir);
     cmd.args(["rewind", "01ARZ3NDEKTSV4RRFFQ69G5FAW", "--list"]);
 
     fabro_snapshot!(context.filters(), cmd, @"

lib/crates/fabro-cli/tests/it/cmd/run.rs

@@ -56,7 +56,7 @@ fn dry_run_simple() {
     ----- stdout -----
     ----- stderr -----
     Workflow: Simple (4 nodes, 3 edges)
-    Graph: ../../../test/simple.fabro
+    Graph: [FIXTURES]/simple.fabro
     Goal: Run tests and report results
 
         Sandbox: local (ready in [TIME])
@@ -80,11 +80,9 @@ fn dry_run_simple() {
 fn dry_run_writes_jsonl_and_live_json() {
     let context = test_context!();
     let run_id = "01ARZ3NDEKTSV4RRFFQ69G5FB8";
-    let workflow = example_fixture("simple.fabro");
 
     context
         .command()
-        .current_dir(&context.temp_dir)
         .args([
             "run",
             "--dry-run",
@@ -93,7 +91,7 @@ fn dry_run_writes_jsonl_and_live_json() {
             "local",
             "--run-id",
             run_id,
-            workflow.to_str().unwrap(),
+            example_fixture("simple.fabro").to_str().unwrap(),
         ])
         .assert()
         .success();
@@ -427,7 +425,7 @@ fn run_id_passthrough_uses_provided_ulid() {
             "--auto-approve",
             "--run-id",
             run_id,
-            "../../../test/simple.fabro",
+            example_fixture("simple.fabro").to_str().unwrap(),
         ])
         .assert()
         .success();
@@ -461,7 +459,6 @@ fn json_run_implies_auto_approve_for_human_gates() {
 
     let output = context
         .command()
-        .current_dir(&context.temp_dir)
         .args([
             "--json",
             "run",
@@ -811,7 +808,7 @@ fn detach_prints_ulid_and_exits() {
         "--detach",
         "--dry-run",
         "--auto-approve",
-        "../../../test/simple.fabro",
+        example_fixture("simple.fabro").to_str().unwrap(),
     ]);
     fabro_snapshot!(context.filters(), cmd, @"
     success: true
@@ -835,7 +832,7 @@ fn detach_creates_run_dir_with_detach_log() {
             "--auto-approve",
             "--run-id",
             run_id,
-            "../../../test/simple.fabro",
+            example_fixture("simple.fabro").to_str().unwrap(),
         ])
         .assert()
         .success();

lib/crates/fabro-cli/tests/it/cmd/start.rs

@@ -163,7 +163,6 @@ fn start_rejects_already_active_or_completed_run() {
     let gate = write_gated_workflow(&context.temp_dir.join("slow.fabro"), "slow", "Run slowly");
 
     let mut create_cmd = context.command();
-    create_cmd.current_dir(&context.temp_dir);
     create_cmd.env("OPENAI_API_KEY", "test");
     create_cmd.args([
         "create",
@@ -185,7 +184,6 @@ fn start_rejects_already_active_or_completed_run() {
     let run = resolve_run(&context, &run_id);
 
     let mut start_cmd = context.command();
-    start_cmd.current_dir(&context.temp_dir);
     start_cmd.env("OPENAI_API_KEY", "test");
     start_cmd.args(["start", &run_id]);
     start_cmd.assert().success();
@@ -193,7 +191,6 @@ fn start_rejects_already_active_or_completed_run() {
     wait_for_status(&run.run_dir, &["running"]);
 
     let mut active_cmd = context.command();
-    active_cmd.current_dir(&context.temp_dir);
     active_cmd.args(["start", &run_id]);
     fabro_snapshot!(context.filters(), active_cmd, @"
     success: false
@@ -207,7 +204,6 @@ fn start_rejects_already_active_or_completed_run() {
     wait_for_status(&run.run_dir, &["succeeded"]);
 
     let mut completed_cmd = context.command();
-    completed_cmd.current_dir(&context.temp_dir);
     completed_cmd.args(["start", &run_id]);
     fabro_snapshot!(context.filters(), completed_cmd, @"
     success: false

lib/crates/fabro-cli/tests/it/cmd/support.rs

@@ -41,7 +41,10 @@ enum GitWorkflowKind {
 }
 
 pub(crate) fn fixture(name: &str) -> PathBuf {
-    Path::new(env!("CARGO_MANIFEST_DIR")).join(format!("../../../test/{name}"))
+    Path::new(env!("CARGO_MANIFEST_DIR"))
+        .join(format!("../../../test/{name}"))
+        .canonicalize()
+        .expect("fixture path should exist")
 }
 
 pub(crate) fn output_stderr(output: &Output) -> String {

lib/crates/fabro-cli/tests/it/cmd/validate.rs

@@ -1,7 +1,10 @@
 use fabro_test::{fabro_snapshot, test_context};
 
 fn fixture(name: &str) -> std::path::PathBuf {
-    std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join(format!("../../../test/{name}"))
+    std::path::Path::new(env!("CARGO_MANIFEST_DIR"))
+        .join(format!("../../../test/{name}"))
+        .canonicalize()
+        .expect("fixture path should exist")
 }
 
 #[test]
@@ -43,7 +46,7 @@ fn simple() {
     ----- stdout -----
     ----- stderr -----
     Workflow: Simple (4 nodes, 3 edges)
-    Graph: ../../../test/simple.fabro
+    Graph: [FIXTURES]/simple.fabro
     Validation: OK
     ");
 }
@@ -59,7 +62,7 @@ fn branching() {
     ----- stdout -----
     ----- stderr -----
     Workflow: Branch (6 nodes, 6 edges)
-    Graph: ../../../test/branching.fabro
+    Graph: [FIXTURES]/branching.fabro
     warning [node: implement]: Node 'implement' has goal_gate=true but no retry_target or fallback_retry_target (goal_gate_has_retry)
     Validation: OK
     ");
@@ -76,7 +79,7 @@ fn conditions() {
     ----- stdout -----
     ----- stderr -----
     Workflow: Conditions (5 nodes, 5 edges)
-    Graph: ../../../test/conditions.fabro
+    Graph: [FIXTURES]/conditions.fabro
     Validation: OK
     ");
 }
@@ -92,7 +95,7 @@ fn parallel() {
     ----- stdout -----
     ----- stderr -----
     Workflow: Parallel (7 nodes, 7 edges)
-    Graph: ../../../test/parallel.fabro
+    Graph: [FIXTURES]/parallel.fabro
     Validation: OK
     ");
 }
@@ -108,7 +111,7 @@ fn styled() {
     ----- stdout -----
     ----- stderr -----
     Workflow: Styled (5 nodes, 4 edges)
-    Graph: ../../../test/styled.fabro
+    Graph: [FIXTURES]/styled.fabro
     Validation: OK
     ");
 }
@@ -124,7 +127,7 @@ fn legacy_tool() {
     ----- stdout -----
     ----- stderr -----
     Workflow: LegacyTool (3 nodes, 2 edges)
-    Graph: ../../../test/legacy_tool.fabro
+    Graph: [FIXTURES]/legacy_tool.fabro
     Validation: OK
     ");
 }
@@ -140,7 +143,7 @@ fn invalid() {
     ----- stdout -----
     ----- stderr -----
     Workflow: Invalid (2 nodes, 1 edges)
-    Graph: ../../../test/invalid.fabro
+    Graph: [FIXTURES]/invalid.fabro
     error: Pipeline must have exactly one start node (shape=Mdiamond or id start/Start) (start_node)
     error [node: exit]: Exit node 'exit' has 1 outgoing edge(s) but must have none (exit_no_outgoing)
     error: Validation failed

lib/crates/fabro-cli/tests/it/cmd/workflow.rs

@@ -43,7 +43,6 @@ fn list() {
 
     let mut cmd = context.command();
     cmd.args(["workflow", "list"]);
-    cmd.current_dir(&context.temp_dir);
     fabro_snapshot!(context.filters(), cmd, @"
     success: true
     exit_code: 0

lib/crates/fabro-cli/tests/it/cmd/workflow_create.rs

@@ -147,7 +147,6 @@ fn workflow_create_rejects_existing_workflow() {
 fn workflow_create_errors_without_project_config() {
     let context = test_context!();
     let mut cmd = context.command();
-    cmd.current_dir(&context.temp_dir);
     cmd.args(["workflow", "create", "hello-world"]);
 
     fabro_snapshot!(context.filters(), cmd, @"

lib/crates/fabro-cli/tests/it/cmd/workflow_list.rs

@@ -31,7 +31,6 @@ fn help() {
 fn workflow_list_errors_without_project_config() {
     let context = test_context!();
     let mut cmd = context.command();
-    cmd.current_dir(&context.temp_dir);
     cmd.args(["workflow", "list"]);
 
     fabro_snapshot!(context.filters(), cmd, @"

lib/crates/fabro-cli/tests/it/scenario/exec.rs

@@ -17,7 +17,6 @@ fn test_exec_creates_file() {
         "claude-haiku-4-5",
         "Create a file called hello.txt containing exactly 'Hello from exec scenario'",
     ]);
-    cmd.current_dir(&context.temp_dir);
     cmd.timeout(Duration::from_secs(120));
     cmd.assert().success();
 

lib/crates/fabro-cli/tests/it/scenario/lifecycle.rs

@@ -2,7 +2,7 @@ use fabro_test::test_context;
 use serde_json::Value;
 
 use super::{fixture, read_json, timeout_for};
-use crate::support::fabro_json_snapshot;
+use crate::support::{example_fixture, fabro_json_snapshot};
 
 #[fabro_macros::e2e_test()]
 fn local_run_lifecycle() {
@@ -112,7 +112,7 @@ fn dry_run_create_start_attach_works_with_default_run_lookup() {
             "--auto-approve",
             "--run-id",
             run_id,
-            "../../../test/simple.fabro",
+            example_fixture("simple.fabro").to_str().unwrap(),
         ])
         .assert()
         .success();
@@ -155,7 +155,7 @@ fn dry_run_detach_attach_works_with_default_run_lookup() {
             "--auto-approve",
             "--run-id",
             run_id,
-            "../../../test/simple.fabro",
+            example_fixture("simple.fabro").to_str().unwrap(),
         ])
         .assert()
         .success();

lib/crates/fabro-cli/tests/it/support/mod.rs

@@ -32,7 +32,10 @@ macro_rules! fabro_json_snapshot {
 pub(crate) use fabro_json_snapshot;
 
 pub(crate) fn example_fixture(name: &str) -> PathBuf {
-    Path::new(env!("CARGO_MANIFEST_DIR")).join(format!("../../../test/{name}"))
+    Path::new(env!("CARGO_MANIFEST_DIR"))
+        .join(format!("../../../test/{name}"))
+        .canonicalize()
+        .expect("fixture path should exist")
 }
 
 pub(crate) fn read_json(path: impl AsRef<Path>) -> Value {

lib/crates/fabro-cli/tests/it/workflow/dry_run_examples.rs

@@ -14,7 +14,7 @@ fn dry_run_branching() {
     ----- stdout -----
     ----- stderr -----
     Workflow: Branch (6 nodes, 6 edges)
-    Graph: ../../../test/branching.fabro
+    Graph: [FIXTURES]/branching.fabro
     Goal: Implement and validate a feature
 
     warning [node: implement]: Node 'implement' has goal_gate=true but no retry_target or fallback_retry_target (goal_gate_has_retry)
@@ -49,7 +49,7 @@ fn dry_run_conditions() {
     ----- stdout -----
     ----- stderr -----
     Workflow: Conditions (5 nodes, 5 edges)
-    Graph: ../../../test/conditions.fabro
+    Graph: [FIXTURES]/conditions.fabro
     Goal: Test condition evaluation with OR and parentheses
 
         Sandbox: local (ready in [TIME])
@@ -81,7 +81,7 @@ fn dry_run_parallel() {
     ----- stdout -----
     ----- stderr -----
     Workflow: Parallel (7 nodes, 7 edges)
-    Graph: ../../../test/parallel.fabro
+    Graph: [FIXTURES]/parallel.fabro
     Goal: Test parallel and fan-in execution
 
         Sandbox: local (ready in [TIME])
@@ -114,7 +114,7 @@ fn dry_run_styled() {
     ----- stdout -----
     ----- stderr -----
     Workflow: Styled (5 nodes, 4 edges)
-    Graph: ../../../test/styled.fabro
+    Graph: [FIXTURES]/styled.fabro
     Goal: Build a styled pipeline
 
         Sandbox: local (ready in [TIME])
@@ -147,7 +147,7 @@ fn dry_run_legacy_tool() {
     ----- stdout -----
     ----- stderr -----
     Workflow: LegacyTool (3 nodes, 2 edges)
-    Graph: ../../../test/legacy_tool.fabro
+    Graph: [FIXTURES]/legacy_tool.fabro
     Goal: Verify backwards compatibility with old tool naming
 
         Sandbox: local (ready in [TIME])

lib/crates/fabro-test/src/lib.rs

@@ -1,9 +1,21 @@
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use std::process::Output;
 
 use assert_cmd::Command;
 use regex::Regex;
 
+/// Walk up from `start` to find the repo-level `test/` fixtures directory.
+pub fn find_test_fixtures_dir(start: &Path) -> Option<PathBuf> {
+    let mut dir = start;
+    loop {
+        let candidate = dir.join("test");
+        if candidate.is_dir() {
+            return candidate.canonicalize().ok();
+        }
+        dir = dir.parent()?;
+    }
+}
+
 /// Static filters applied to every snapshot.
 static INSTA_FILTERS: &[(&str, &str)] = &[
     (r"fabro \d+\.\d+\.\d+", "fabro [VERSION]"),
@@ -127,6 +139,12 @@ impl TestContext {
         }
     }
 
+    /// Register a custom filter (regex pattern → replacement).
+    pub fn add_filter(&mut self, pattern: &str, replacement: &str) {
+        self.filters
+            .push((regex::escape(pattern), replacement.to_string()));
+    }
+
     /// Returns the combined static + context-specific filters.
     pub fn filters(&self) -> Vec<(String, String)> {
         let mut filters = self.filters.clone();
@@ -139,8 +157,14 @@ impl TestContext {
     }
 
     /// Build a base `Command` with all isolation env vars set.
+    ///
+    /// The working directory defaults to `self.temp_dir` (a non-git temp
+    /// directory) so tests never accidentally interact with the real repo.
+    /// Tests that need a specific working directory can override this with
+    /// a subsequent `.current_dir(path)` call.
     pub fn command(&self) -> Command {
         let mut cmd = Command::new(&self.fabro_bin);
+        cmd.current_dir(&self.temp_dir);
         cmd.env("NO_COLOR", "1");
         cmd.env("HOME", &self.home_dir);
         cmd.env("FABRO_NO_UPGRADE_CHECK", "true");
@@ -399,11 +423,21 @@ pub fn apply_filters(snapshot: &str, filters: &[(String, String)]) -> String {
 }
 
 /// Create a `TestContext` using the `fabro` binary built by cargo.
+///
+/// Automatically registers a `[FIXTURES]` snapshot filter for the `test/`
+/// directory at the repository root (found by walking up from `CARGO_MANIFEST_DIR`).
 #[macro_export]
 macro_rules! test_context {
-    () => {
-        $crate::TestContext::new(std::path::PathBuf::from(env!("CARGO_BIN_EXE_fabro")))
-    };
+    () => {{
+        let mut ctx =
+            $crate::TestContext::new(std::path::PathBuf::from(env!("CARGO_BIN_EXE_fabro")));
+        if let Some(fixtures_dir) =
+            $crate::find_test_fixtures_dir(std::path::Path::new(env!("CARGO_MANIFEST_DIR")))
+        {
+            ctx.add_filter(fixtures_dir.to_str().unwrap(), "[FIXTURES]");
+        }
+        ctx
+    }};
 }
 
 /// Snapshot test macro that runs a command and compares output using insta.