testers.testEqualContents: init

1 files changed, 24 insertions, 0 deletions

diff --git a/doc/builders/testers.chapter.md b/doc/builders/testers.chapter.md
index 57f66a428482d..58bb06f231378 100644
--- a/doc/builders/testers.chapter.md
+++ b/doc/builders/testers.chapter.md
@@ -75,6 +75,30 @@ environment to a minimum, some small changes are inevitable.
    `buildPackages.coreutils` and possibly more. These are not added to `PATH`
    or any other environment variable, so they should be hard to observe.
 
+## `testEqualContents` {#tester-equalContents}
+
+Check that two paths have the same contents.
+
+Example:
+
+```nix
+testers.testEqualContents {
+  assertion = "sed -e performs replacement";
+  expected = writeText "expected" ''
+    foo baz baz
+  '';
+  actual = runCommand "actual" {
+    # not really necessary for a package that's in stdenv
+    nativeBuildInputs = [ gnused ];
+    base = writeText "base" ''
+      foo bar baz
+    '';
+  } ''
+    sed -e 's/bar/baz/g' $base >$out
+  '';
+}
+```
+
 ## `testEqualDerivation` {#tester-testEqualDerivation}
 
 Checks that two packages produce the exact same build instructions.