diff --git a/lib/std/private/gitutils.nim b/lib/std/private/gitutils.nim
index db0c607255..16eaf3580f 100644
--- a/lib/std/private/gitutils.nim
+++ b/lib/std/private/gitutils.nim
@@ -39,14 +39,27 @@ proc isGitRepo*(dir: string): bool =
   # remove trailing whitespaces from the result.
   result = status == 0 and output.strip() == ""
 
-proc diffStrings*(a, b: string): string =
+proc diffFiles*(path1, path2: string): tuple[output: string, same: bool] =
+  # could be customized, e.g. non-git diff with `diff -uNdr`, or with git diff options (e.g. --color-moved, --word-diff).
+  # in general, git diff has more options.
+  var status = 0
+  (result.output, status) = execCmdEx("git diff --no-index $1 $2" % [path1.quoteShell, path2.quoteShell])
+  doAssert (status == 0) or (status == 1)
+  result.same = status == 0
+
+proc diffStrings*(a, b: string): tuple[output: string, same: bool] =
   runnableExamples:
-    let a = "ok1\nok2\nok3"
-    let b = "ok1\nok2 alt\nok3"
-    let c = diffStrings(a, b)
-    echo c
-    let c2 = diffStrings(a, a)
-    echo c2
+    let a = "ok1\nok2\nok3\n"
+    let b = "ok1\nok2 alt\nok3\nok4\n"
+    let (c, same) = diffStrings(a, b)
+    doAssert not same
+    let (c2, same2) = diffStrings(a, a)
+    doAssert same2
+
+  runnableExamples("-r:off"):
+    let a = "ok1\nok2\nok3\n"
+    let b = "ok1\nok2 alt\nok3\nok4\n"
+    echo diffStrings(a, b).output
 
   template tmpFileImpl(prefix, str): auto =
     # pending https://github.com/nim-lang/Nim/pull/17889
@@ -59,7 +72,4 @@ proc diffStrings*(a, b: string): string =
   defer:
     removeFile(patha)
     removeFile(pathb)
-  # could be customized, e.g. non-git diff with `diff -uNdr`, or with git diff options.
-  var status = 0
-  (result, status) = execCmdEx("git diff --no-index $1 $2" % [patha.quoteShell, pathb.quoteShell])
-  echo status
+  result = diffFiles(patha, pathb)
diff --git a/nimdoc/rsttester.nim b/nimdoc/rsttester.nim
index 6d41ffb86b..daca3dfc76 100644
--- a/nimdoc/rsttester.nim
+++ b/nimdoc/rsttester.nim
@@ -1,4 +1,5 @@
 import os, strutils
+from std/private/gitutils import diffFiles
 
 const
   baseDir = "nimdoc/rst2html"
@@ -19,7 +20,7 @@ proc testRst2Html(fixup = false) =
     exec("$1 rst2html $2" % [nimExe, sourceFile])
     let producedHtml = expectedHtml.replace('\\', '/').replace("/expected/", "/source/htmldocs/")
     if readFile(expectedHtml) != readFile(producedHtml):
-      discard execShellCmd("diff -uNdr " & expectedHtml & " " & producedHtml)
+      echo diffFiles(expectedHtml, producedHtml).output
       inc failures
       if fixup:
         copyFile(producedHtml, expectedHtml)
diff --git a/nimdoc/tester.nim b/nimdoc/tester.nim
index 5262952224..9daa0bb51e 100644
--- a/nimdoc/tester.nim
+++ b/nimdoc/tester.nim
@@ -3,6 +3,7 @@
 # to change expected results (after carefully verifying everything), use -d:fixup
 
 import strutils, os
+from std/private/gitutils import diffFiles
 
 var
   failures = 0
@@ -40,7 +41,7 @@ proc testNimDoc(prjDir, docsDir: string; switches: NimSwitches; fixup = false) =
       inc failures
     elif readFile(expected) != readFile(produced):
       echo "FAILURE: files differ: ", produced
-      discard execShellCmd("diff -uNdr " & expected & " " & produced)
+      echo diffFiles(expected, produced).output
       inc failures
       if fixup:
         copyFile(produced, expected)
diff --git a/nimpretty/tester.nim b/nimpretty/tester.nim
index 0a60ce6935..b1f15aee61 100644
--- a/nimpretty/tester.nim
+++ b/nimpretty/tester.nim
@@ -1,6 +1,7 @@
 # Small program that runs the test cases
 
 import strutils, os, sequtils
+from std/private/gitutils import diffFiles
 
 const
   dir = "nimpretty/tests"
@@ -26,7 +27,7 @@ proc test(infile, ext: string) =
   let produced = dir / nimFile.changeFileExt(ext)
   if readFile(expected) != readFile(produced):
     echo "FAILURE: files differ: ", nimFile
-    discard execShellCmd("diff -uNdr " & expected & " " & produced)
+    echo diffFiles(expected, produced).output
     failures += 1
   else:
     echo "SUCCESS: files identical: ", nimFile
@@ -43,7 +44,7 @@ proc testTogether(infiles: seq[string]) =
     let produced = dir / "outputdir" / infile
     if readFile(expected) != readFile(produced):
       echo "FAILURE: files differ: ", nimFile
-      discard execShellCmd("diff -uNdr " & expected & " " & produced)
+      echo diffFiles(expected, produced).output
       failures += 1
     else:
       echo "SUCCESS: files identical: ", nimFile
diff --git a/testament/categories.nim b/testament/categories.nim
index ffee5eeb39..f1dee35708 100644
--- a/testament/categories.nim
+++ b/testament/categories.nim
@@ -665,8 +665,8 @@ proc runJoinedTest(r: var TResults, cat: Category, testsDir: string, options: st
 
   if buf != outputExpected:
     writeFile(outputExceptedFile, outputExpected)
-    discard execShellCmd("diff -uNdr $1 $2" % [outputExceptedFile, outputGottenFile])
-    echo failString & "megatest output different!"
+    echo diffFiles(outputGottenFile, outputExceptedFile).output
+    echo failString & "megatest output different, see $1 vs $2" % [outputGottenFile, outputExceptedFile]
     # outputGottenFile, outputExceptedFile not removed on purpose for debugging.
     quit 1
   else:
diff --git a/testament/testament.nim b/testament/testament.nim
index 9caa3f6b9b..0607ac41d1 100644
--- a/testament/testament.nim
+++ b/testament/testament.nim
@@ -17,6 +17,7 @@ from std/sugar import dup
 import compiler/nodejs
 import lib/stdtest/testutils
 from lib/stdtest/specialpaths import splitTestFile
+from std/private/gitutils import diffStrings
 
 proc trimUnitSep(x: var string) =
   let L = x.len
@@ -307,7 +308,7 @@ proc addResult(r: var TResults, test: TTest, target: TTarget,
       maybeStyledEcho styleBright, expected, "\n"
       maybeStyledEcho fgYellow, "Gotten:"
       maybeStyledEcho styleBright, given, "\n"
-
+      echo diffStrings(expected, given).output
 
   if backendLogging and (isAppVeyor or isAzure):
     let (outcome, msg) =