diff --git a/lib/tests/fetchers.nix b/lib/tests/fetchers.nix
new file mode 100644
index 000000000000..c36da35673a7
--- /dev/null
+++ b/lib/tests/fetchers.nix
@@ -0,0 +1,165 @@
+let
+  lib = import ./..;
+
+  inherit (lib)
+    fakeHash
+    fakeSha256
+    fakeSha512
+    flip
+    functionArgs
+    runTests
+    ;
+  inherit (lib.fetchers) normalizeHash withNormalizedHash;
+
+  testingThrow = expr: {
+    expr = with builtins; tryEval (seq expr "didn't throw");
+    expected = {
+      success = false;
+      value = false;
+    };
+  };
+
+  # hashes of empty
+  sri256 = "sha256-d6xi4mKdjkX2JFicDIv5niSzpyI0m/Hnm8GGAIU04kY=";
+  sri512 = "sha512-AXFyVo7jiZ5we10fxZ5E9qfPjSfqkizY2apCzORKFVYZaNhCIVbooY+J4cYST00ztLf0EjivIBPPdtIYFUMfzQ==";
+
+  unionOfDisjoints = lib.foldl lib.attrsets.unionOfDisjoint { };
+
+  genTests = n: f: {
+    "test${n}AlreadyNormalized" = {
+      expr = f { } {
+        outputHash = "";
+        outputHashAlgo = "md42";
+      };
+      expected = {
+        outputHash = "";
+        outputHashAlgo = "md42";
+      };
+    };
+
+    "test${n}EmptySha256" = {
+      expr = f { } { sha256 = ""; };
+      expected = {
+        outputHash = fakeSha256;
+        outputHashAlgo = "sha256";
+      };
+    };
+
+    "test${n}EmptySha512" = {
+      expr = f { hashTypes = [ "sha512" ]; } { sha512 = ""; };
+      expected = {
+        outputHash = fakeSha512;
+        outputHashAlgo = "sha512";
+      };
+    };
+
+    "test${n}EmptyHash" = {
+      expr = f { } { hash = ""; };
+      expected = {
+        outputHash = fakeHash;
+        outputHashAlgo = null;
+      };
+    };
+
+    "test${n}Sri256" = {
+      expr = f { } { hash = sri256; };
+      expected = {
+        outputHash = sri256;
+        outputHashAlgo = null;
+      };
+    };
+
+    "test${n}Sri512" = {
+      expr = f { } { hash = sri512; };
+      expected = {
+        outputHash = sri512;
+        outputHashAlgo = null;
+      };
+    };
+
+    "test${n}PreservesAttrs" = {
+      expr = f { } {
+        hash = "aaaa";
+        destination = "Earth";
+      };
+      expected = {
+        outputHash = "aaaa";
+        outputHashAlgo = null;
+        destination = "Earth";
+      };
+    };
+
+    "test${n}RejectsSha1ByDefault" = testingThrow (f { } { sha1 = ""; });
+    "test${n}RejectsSha512ByDefault" = testingThrow (f { } { sha512 = ""; });
+
+    "test${n}ThrowsOnMissing" = testingThrow (f { } { gibi = false; });
+  };
+in
+runTests (unionOfDisjoints [
+  (genTests "NormalizeHash" normalizeHash)
+  (genTests "WithNormalized" (
+    flip withNormalizedHash ({ outputHash, outputHashAlgo, ... }@args: args)
+  ))
+  {
+    testNormalizeNotRequiredEquivalent = {
+      expr = normalizeHash { required = false; } {
+        hash = "";
+        prof = "shadoko";
+      };
+      expected = normalizeHash { } {
+        hash = "";
+        prof = "shadoko";
+      };
+    };
+
+    testNormalizeNotRequiredPassthru = {
+      expr = normalizeHash { required = false; } { "ga bu" = "zo meu"; };
+      expected."ga bu" = "zo meu";
+    };
+
+    testOptionalArg = {
+      expr = withNormalizedHash { } (
+        {
+          outputHash ? "",
+          outputHashAlgo ? null,
+          ...
+        }@args:
+        args
+      ) { author = "Jacques Rouxel"; };
+      expected.author = "Jacques Rouxel";
+    };
+
+    testOptionalArgMetadata = {
+      expr = functionArgs (
+        withNormalizedHash { } (
+          {
+            outputHash ? "",
+            outputHashAlgo ? null,
+          }:
+          { }
+        )
+      );
+      expected.hash = true;
+    };
+
+    testPreservesArgsMetadata = {
+      expr = functionArgs (
+        withNormalizedHash { } (
+          {
+            outputHash,
+            outputHashAlgo,
+            pumping ? true,
+          }:
+          { }
+        )
+      );
+      expected = {
+        hash = false;
+        pumping = true;
+      };
+    };
+
+    testRejectsMissingHashArg = testingThrow (withNormalizedHash { } ({ outputHashAlgo }: { }));
+    testRejectsMissingAlgoArg = testingThrow (withNormalizedHash { } ({ outputHash }: { }));
+  }
+])
diff --git a/lib/tests/test-with-nix.nix b/lib/tests/test-with-nix.nix
index 63b4b10bae8c..1316aaa49b88 100644
--- a/lib/tests/test-with-nix.nix
+++ b/lib/tests/test-with-nix.nix
@@ -17,6 +17,7 @@
 pkgs.runCommand "nixpkgs-lib-tests-nix-${nix.version}" {
   buildInputs = [
     (import ./check-eval.nix)
+    (import ./fetchers.nix)
     (import ./maintainers.nix {
       inherit pkgs;
       lib = import ../.;