diff --git a/lib/experimental/diff.nim b/lib/experimental/diff.nim
index 5a69687a3a1c..d1274d771ccb 100644
--- a/lib/experimental/diff.nim
+++ b/lib/experimental/diff.nim
@@ -331,83 +331,3 @@ proc diffText*(textA, textB: string): seq[Item] =
   optimize(dataA)
   optimize(dataB)
   result = createDiffs(dataA, dataB)
-
-when isMainModule:
-
-  proc testHelper(f: seq[Item]): string =
-    for it in f:
-      result.add(
-        $it.deletedA & "." & $it.insertedB & "." & $it.startA & "." & $it.startB & "*"
-      )
-
-  proc main() =
-    var a, b: string
-
-    stdout.writeLine("Diff Self Test...")
-
-    # test all changes
-    a = "a,b,c,d,e,f,g,h,i,j,k,l".replace(',', '\n')
-    b = "0,1,2,3,4,5,6,7,8,9".replace(',', '\n')
-    assert(testHelper(diffText(a, b)) ==
-      "12.10.0.0*",
-      "all-changes test failed.")
-    stdout.writeLine("all-changes test passed.")
-    # test all same
-    a = "a,b,c,d,e,f,g,h,i,j,k,l".replace(',', '\n')
-    b = a
-    assert(testHelper(diffText(a, b)) ==
-      "",
-      "all-same test failed.")
-    stdout.writeLine("all-same test passed.")
-
-    # test snake
-    a = "a,b,c,d,e,f".replace(',', '\n')
-    b = "b,c,d,e,f,x".replace(',', '\n')
-    assert(testHelper(diffText(a, b)) ==
-      "1.0.0.0*0.1.6.5*",
-      "snake test failed.")
-    stdout.writeLine("snake test passed.")
-
-    # 2002.09.20 - repro
-    a = "c1,a,c2,b,c,d,e,g,h,i,j,c3,k,l".replace(',', '\n')
-    b = "C1,a,C2,b,c,d,e,I1,e,g,h,i,j,C3,k,I2,l".replace(',', '\n')
-    assert(testHelper(diffText(a, b)) ==
-      "1.1.0.0*1.1.2.2*0.2.7.7*1.1.11.13*0.1.13.15*",
-      "repro20020920 test failed.")
-    stdout.writeLine("repro20020920 test passed.")
-
-    # 2003.02.07 - repro
-    a = "F".replace(',', '\n')
-    b = "0,F,1,2,3,4,5,6,7".replace(',', '\n')
-    assert(testHelper(diffText(a, b)) ==
-      "0.1.0.0*0.7.1.2*",
-      "repro20030207 test failed.")
-    stdout.writeLine("repro20030207 test passed.")
-
-    # Muegel - repro
-    a = "HELLO\nWORLD"
-    b = "\n\nhello\n\n\n\nworld\n"
-    assert(testHelper(diffText(a, b)) ==
-      "2.8.0.0*",
-      "repro20030409 test failed.")
-    stdout.writeLine("repro20030409 test passed.")
-
-    # test some differences
-    a = "a,b,-,c,d,e,f,f".replace(',', '\n')
-    b = "a,b,x,c,e,f".replace(',', '\n')
-    assert(testHelper(diffText(a, b)) ==
-      "1.1.2.2*1.0.4.4*1.0.7.6*",
-      "some-changes test failed.")
-    stdout.writeLine("some-changes test passed.")
-
-    # test one change within long chain of repeats
-    a = "a,a,a,a,a,a,a,a,a,a".replace(',', '\n')
-    b = "a,a,a,a,-,a,a,a,a,a".replace(',', '\n')
-    assert(testHelper(diffText(a, b)) ==
-      "0.1.4.4*1.0.9.10*",
-      "long chain of repeats test failed.")
-
-    stdout.writeLine("End.")
-    stdout.flushFile
-
-  main()
diff --git a/tests/stdlib/tdiff.nim b/tests/stdlib/tdiff.nim
new file mode 100644
index 000000000000..05777d89c758
--- /dev/null
+++ b/tests/stdlib/tdiff.nim
@@ -0,0 +1,73 @@
+discard """
+  targets: "c js"
+"""
+
+import experimental/diff
+import std/strutils
+
+proc testHelper(f: seq[Item]): string =
+  for it in f:
+    result.add(
+      $it.deletedA & "." & $it.insertedB & "." & $it.startA & "." & $it.startB & "*"
+    )
+
+template main() =
+  var a, b: string
+
+  # Diff Self Test
+  # test all changes
+  a = "a,b,c,d,e,f,g,h,i,j,k,l".replace(',', '\n')
+  b = "0,1,2,3,4,5,6,7,8,9".replace(',', '\n')
+  doAssert(testHelper(diffText(a, b)) ==
+    "12.10.0.0*",
+    "all-changes test failed.")
+  # test all same
+  a = "a,b,c,d,e,f,g,h,i,j,k,l".replace(',', '\n')
+  b = a
+  doAssert(testHelper(diffText(a, b)) ==
+    "",
+    "all-same test failed.")
+
+  # test snake
+  a = "a,b,c,d,e,f".replace(',', '\n')
+  b = "b,c,d,e,f,x".replace(',', '\n')
+  doAssert(testHelper(diffText(a, b)) ==
+    "1.0.0.0*0.1.6.5*",
+    "snake test failed.")
+
+  # 2002.09.20 - repro
+  a = "c1,a,c2,b,c,d,e,g,h,i,j,c3,k,l".replace(',', '\n')
+  b = "C1,a,C2,b,c,d,e,I1,e,g,h,i,j,C3,k,I2,l".replace(',', '\n')
+  doAssert(testHelper(diffText(a, b)) ==
+    "1.1.0.0*1.1.2.2*0.2.7.7*1.1.11.13*0.1.13.15*",
+    "repro20020920 test failed.")
+
+  # 2003.02.07 - repro
+  a = "F".replace(',', '\n')
+  b = "0,F,1,2,3,4,5,6,7".replace(',', '\n')
+  doAssert(testHelper(diffText(a, b)) ==
+    "0.1.0.0*0.7.1.2*",
+    "repro20030207 test failed.")
+
+  # Muegel - repro
+  a = "HELLO\nWORLD"
+  b = "\n\nhello\n\n\n\nworld\n"
+  doAssert(testHelper(diffText(a, b)) ==
+    "2.8.0.0*",
+    "repro20030409 test failed.")
+
+  # test some differences
+  a = "a,b,-,c,d,e,f,f".replace(',', '\n')
+  b = "a,b,x,c,e,f".replace(',', '\n')
+  doAssert(testHelper(diffText(a, b)) ==
+    "1.1.2.2*1.0.4.4*1.0.7.6*",
+    "some-changes test failed.")
+
+  # test one change within long chain of repeats
+  a = "a,a,a,a,a,a,a,a,a,a".replace(',', '\n')
+  b = "a,a,a,a,-,a,a,a,a,a".replace(',', '\n')
+  doAssert(testHelper(diffText(a, b)) ==
+    "0.1.4.4*1.0.9.10*",
+    "long chain of repeats test failed.")
+main()
+static: main()