match tool outputs whole instead of probing fragments

Substring assertions on llmxml renders let regressions in any
unprobed attribute or line pass unnoticed; the rendered text is the
product contract a model reads, so it is now pinned byte for byte.
Multi-line renders compare against golden files (regenerate with
go test ./internal/tools/ -update and review the diff); one-line acks
compare inline. Error-path assertions stay substring-based -- error
wording is not a contract.

Wire-path assertions tightened to exact equality alongside, which
immediately surfaced a detail Contains had hidden: the files listing
request ends with a trailing slash.

Author: xobotyi

internal/gerritclient/review_test.go

@@ -72,7 +72,7 @@ func Test_SetReview_Gating(t *testing.T) {
 		require.NoError(t, err)
 
 		require.Len(t, *posts, 1)
-		assert.Contains(t, (*posts)[0], "/revisions/current/review")
+		assert.Equal(t, "/a/changes/123/revisions/current/review", (*posts)[0])
 	})
 
 	t.Run("foreign change refused by default", func(t *testing.T) {

internal/gerritclient/scoping_test.go

@@ -146,7 +146,7 @@ func Test_ProjectScoping(t *testing.T) {
 
 		assert.NotNil(t, files)
 		require.Len(t, *requests, 1)
-		assert.Contains(t, (*requests)[0], "/files")
+		assert.Equal(t, "/a/changes/core~123/revisions/current/files/", (*requests)[0])
 	})
 
 	t.Run("unscoped client passes everything through", func(t *testing.T) {

internal/tools/get-change_test.go

@@ -137,24 +137,7 @@ func Test_GetChange(t *testing.T) {
 		text, ok := res.Content[0].(*mcp.TextContent)
 		require.True(t, ok)
 
-		for _, part := range []string{
-			`<change number="123"`,
-			`project="core"`,
-			`status="NEW"`,
-			`owner="Alice (alice)"`,
-			`submittable="true"`,
-			`current_revision="abc123def"`,
-			"<subject>Fix nil deref in scanner</subject>",
-			`<label name="Code-Review">`,
-			`<vote value="2" by="Bob (bob)"/>`,
-			`<reviewer state="REVIEWER">Bob (bob)</reviewer>`,
-			`<message author="Bob (bob)"`,
-			"Looks good to me",
-		} {
-			assert.Contains(t, text.Text, part)
-		}
-
-		assert.NotContains(t, text.Text, "Carol", "zero votes must not render")
+		golden(t, "get-change", text.Text)
 
 		wantOpts := []string{"DETAILED_LABELS", "DETAILED_ACCOUNTS", "CURRENT_REVISION", "MESSAGES", "SUBMITTABLE"}
 		for _, opt := range wantOpts {

internal/tools/golden_test.go

@@ -0,0 +1,34 @@
+package tools_test
+
+import (
+	"flag"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+//nolint:gochecknoglobals // test binary flag, must register at package init
+var update = flag.Bool("update", false, "rewrite golden files with actual tool output")
+
+// golden asserts that got matches testdata/<name>.golden byte for byte. Tool
+// output is the product contract — the rendered llmxml is exactly what a
+// model reads — so renders are pinned whole, not probed for fragments.
+// Running the package tests with -update rewrites the files from actual
+// output; review the diff before committing.
+func golden(t *testing.T, name, got string) {
+	t.Helper()
+
+	path := filepath.Join("testdata", name+".golden")
+
+	if *update {
+		require.NoError(t, os.MkdirAll(filepath.Dir(path), 0o750))
+		require.NoError(t, os.WriteFile(path, []byte(got), 0o600))
+	}
+
+	want, err := os.ReadFile(path) //nolint:gosec // path is test-owned: testdata/<name>.golden
+	require.NoError(t, err, "missing golden file; regenerate with: go test ./internal/tools/ -update")
+	assert.Equal(t, string(want), got)
+}

internal/tools/post-comments_test.go

@@ -74,7 +74,7 @@ func Test_PostComments(t *testing.T) {
 			},
 		})
 
-		assert.Contains(t, out, `<review_posted change="123" message="true" comments="3" notify="OWNER"/>`)
+		assert.Equal(t, `<review_posted change="123" message="true" comments="3" notify="OWNER"/>`, out)
 
 		assert.Equal(t, "Overall: looks solid", (*body)["message"])
 		assert.Equal(t, "OWNER", (*body)["notify"])

internal/tools/read-tools_test.go

@@ -2,7 +2,6 @@ package tools_test
 
 import (
 	"net/http"
-	"strings"
 	"testing"
 
 	"github.com/modelcontextprotocol/go-sdk/mcp"
@@ -64,17 +63,7 @@ func Test_SearchChanges(t *testing.T) {
 
 	out := callTool(t, cs, "search_changes", map[string]any{"query": "status:open owner:self"})
 
-	for _, part := range []string{
-		`<changes query="status:open owner:self"`,
-		`count="2"`,
-		`more="true"`,
-		`<change number="1"`,
-		`owner="Alice (alice)"`,
-		`>First</change>`,
-		`status="MERGED"`,
-	} {
-		assert.Contains(t, out, part)
-	}
+	golden(t, "search-changes", out)
 
 	assert.Contains(t, *lastURL, "q=status")
 	assert.Contains(t, *lastURL, "n=25", "default limit applies")
@@ -95,21 +84,9 @@ func Test_ListChangeFiles(t *testing.T) {
 
 	out := callTool(t, cs, "list_change_files", map[string]any{"change": "123"})
 
-	for _, part := range []string{
-		`<files change="123" revision="current" count="4">`,
-		`<file path="/COMMIT_MSG" status="A"`,
-		`<file path="core/scanner.go" status="M" insertions="5" deletions="2"/>`,
-		`binary="true"`,
-		`old_path="core/old.go"`,
-	} {
-		assert.Contains(t, out, part)
-	}
+	golden(t, "list-change-files", out)
 
 	assert.Contains(t, *lastURL, "/a/changes/123/revisions/current/files")
-
-	logoIdx := strings.Index(out, "assets/logo.png")
-	scannerIdx := strings.Index(out, "core/scanner.go")
-	assert.Less(t, logoIdx, scannerIdx, "files sorted by path")
 }
 
 func Test_GetFileDiff(t *testing.T) {
@@ -135,16 +112,7 @@ func Test_GetFileDiff(t *testing.T) {
 			"change": "123", "file": "core/scanner.go", "revision": "2",
 		})
 
-		for _, part := range []string{
-			`<diff change="123" revision="2" file="core/scanner.go" change_type="MODIFIED">`,
-			"... 40 common lines skipped ...",
-			" func scan() {",
-			"-\told := 1",
-			"+\tnew := 2",
-			"+\textra := 3",
-		} {
-			assert.Contains(t, out, part)
-		}
+		golden(t, "file-diff-text", out)
 
 		assert.Contains(t, *lastURL, "/a/changes/123/revisions/2/files/core%2Fscanner.go/diff")
 	})
@@ -158,8 +126,7 @@ func Test_GetFileDiff(t *testing.T) {
 
 		out := callTool(t, cs, "get_file_diff", map[string]any{"change": "123", "file": "logo.png"})
 
-		assert.Contains(t, out, `binary="true"`)
-		assert.Contains(t, out, "/>")
+		golden(t, "file-diff-binary", out)
 	})
 }
 
@@ -194,24 +161,9 @@ func Test_GetChangeComments(t *testing.T) {
 
 		out := callTool(t, cs, "get_change_comments", map[string]any{"change": "123"})
 
-		for _, part := range []string{
-			`<comments change="123" filter="all" threads="3">`,
-			`<thread resolved="true">`,
-			`<thread resolved="false">`,
-			`<comment id="c1"`,
-			`in_reply_to="c1"`,
-			`lines="20-25"`,
-			"Is this nil-safe?",
-			"Orphan reply",
-		} {
-			assert.Contains(t, out, part)
-		}
+		golden(t, "change-comments-all", out)
 
 		assert.Contains(t, *lastURL, "/a/changes/123/comments")
-
-		c1 := strings.Index(out, `<comment id="c1"`)
-		c2 := strings.Index(out, `<comment id="c2"`)
-		assert.Less(t, c1, c2, "replies follow their root chronologically")
 	})
 
 	t.Run("unresolved filter drops resolved threads", func(t *testing.T) {
@@ -221,10 +173,7 @@ func Test_GetChangeComments(t *testing.T) {
 
 		out := callTool(t, cs, "get_change_comments", map[string]any{"change": "123", "status": "unresolved"})
 
-		assert.Contains(t, out, `threads="1"`)
-		assert.Contains(t, out, "This block races")
-		assert.NotContains(t, out, "Is this nil-safe?")
-		assert.NotContains(t, out, "Orphan reply")
+		golden(t, "change-comments-unresolved", out)
 	})
 
 	t.Run("invalid filter is an error", func(t *testing.T) {

internal/tools/set-vote_test.go

@@ -66,7 +66,7 @@ func Test_SetVote(t *testing.T) {
 			"message": "lgtm",
 		})
 
-		assert.Contains(t, out, `<vote_set change="123" label="Code-Review" value="2"/>`)
+		assert.Equal(t, `<vote_set change="123" label="Code-Review" value="2"/>`, out)
 
 		assert.Equal(t, "lgtm", (*body)["message"])
 		assert.Equal(t, map[string]any{"Code-Review": float64(2)}, (*body)["labels"])

internal/tools/testdata/change-comments-all.golden

@@ -0,0 +1,24 @@
+<comments change="123" filter="all" threads="3">
+<file path="core/scanner.go">
+<thread resolved="true">
+<comment id="c1" author="Bob (bob)" date="2026-07-01T10:00:00Z" patch_set="1" line="10">
+Is this nil-safe?
+</comment>
+<comment id="c2" author="Alice (alice)" date="2026-07-01T11:00:00Z" patch_set="1" line="10" in_reply_to="c1">
+Fixed in ps2
+</comment>
+</thread>
+<thread resolved="false">
+<comment id="c3" author="Bob (bob)" date="2026-07-02T09:00:00Z" patch_set="2" lines="20-25">
+This block races
+</comment>
+</thread>
+</file>
+<file path="docs/readme.md">
+<thread resolved="true">
+<comment id="c4" author="Alice (alice)" date="2026-07-01T12:00:00Z" line="1" in_reply_to="gone">
+Orphan reply
+</comment>
+</thread>
+</file>
+</comments>

internal/tools/testdata/change-comments-unresolved.golden

@@ -0,0 +1,9 @@
+<comments change="123" filter="unresolved" threads="1">
+<file path="core/scanner.go">
+<thread resolved="false">
+<comment id="c3" author="Bob (bob)" date="2026-07-02T09:00:00Z" patch_set="2" lines="20-25">
+This block races
+</comment>
+</thread>
+</file>
+</comments>

internal/tools/testdata/file-diff-binary.golden

@@ -0,0 +1 @@
+<diff change="123" revision="current" file="logo.png" change_type="ADDED" binary="true"/>