doc: move testers to their own chapter

7 files changed, 87 insertions, 75 deletions

diff --git a/doc/builders/fetchers.chapter.md b/doc/builders/fetchers.chapter.md
index d9f22b06282..09a41cd9ce0 100644
--- a/doc/builders/fetchers.chapter.md
+++ b/doc/builders/fetchers.chapter.md
@@ -6,7 +6,7 @@ When using Nix, you will frequently need to download source code and other files
 
 Because fixed output derivations are _identified_ by their hash, a common mistake is to update a fetcher's URL or a version parameter, without updating the hash. **This will cause the old contents to be used.** So remember to always invalidate the hash argument.
 
-For those who develop and maintain fetchers, a similar problem arises with changes to the implementation of a fetcher. These may cause a fixed output derivation to fail, but won't normally be caught by tests because the supposed output is already in the store or cache. For the purpose of testing, you can use a trick that is embodied by the [`invalidateFetcherByDrvHash`](#sec-pkgs-invalidateFetcherByDrvHash) function. It uses the derivation `name` to create a unique output path per fetcher implementation, defeating the caching precisely where it would be harmful.
+For those who develop and maintain fetchers, a similar problem arises with changes to the implementation of a fetcher. These may cause a fixed output derivation to fail, but won't normally be caught by tests because the supposed output is already in the store or cache. For the purpose of testing, you can use a trick that is embodied by the [`invalidateFetcherByDrvHash`](#tester-invalidateFetcherByDrvHash) function. It uses the derivation `name` to create a unique output path per fetcher implementation, defeating the caching precisely where it would be harmful.
 
 ## `fetchurl` and `fetchzip` {#fetchurl}
 
diff --git a/doc/builders/special.xml b/doc/builders/special.xml
index 2f84599cdd4..8902ce5c813 100644
--- a/doc/builders/special.xml
+++ b/doc/builders/special.xml
@@ -7,5 +7,4 @@
  </para>
  <xi:include href="special/fhs-environments.section.xml" />
  <xi:include href="special/mkshell.section.xml" />
- <xi:include href="special/invalidateFetcherByDrvHash.section.xml" />
 </chapter>
diff --git a/doc/builders/special/invalidateFetcherByDrvHash.section.md b/doc/builders/special/invalidateFetcherByDrvHash.section.md
deleted file mode 100644
index 7c2f03a64b7..00000000000
--- a/doc/builders/special/invalidateFetcherByDrvHash.section.md
+++ /dev/null
@@ -1,31 +0,0 @@
-
-## `invalidateFetcherByDrvHash` {#sec-pkgs-invalidateFetcherByDrvHash}
-
-Use the derivation hash to invalidate the output via name, for testing.
-
-Type: `(a@{ name, ... } -> Derivation) -> a -> Derivation`
-
-Normally, fixed output derivations can and should be cached by their output
-hash only, but for testing we want to re-fetch everytime the fetcher changes.
-
-Changes to the fetcher become apparent in the drvPath, which is a hash of
-how to fetch, rather than a fixed store path.
-By inserting this hash into the name, we can make sure to re-run the fetcher
-every time the fetcher changes.
-
-This relies on the assumption that Nix isn't clever enough to reuse its
-database of local store contents to optimize fetching.
-
-You might notice that the "salted" name derives from the normal invocation,
-not the final derivation. `invalidateFetcherByDrvHash` has to invoke the fetcher
-function twice: once to get a derivation hash, and again to produce the final
-fixed output derivation.
-
-Example:
-
-    tests.fetchgit = invalidateFetcherByDrvHash fetchgit {
-      name = "nix-source";
-      url = "https://github.com/NixOS/nix";
-      rev = "9d9dbe6ed05854e03811c361a3380e09183f4f4a";
-      sha256 = "sha256-7DszvbCNTjpzGRmpIVAWXk20P0/XTrWZ79KSOGLrUWY=";
-    };
diff --git a/doc/builders/testers.chapter.md b/doc/builders/testers.chapter.md
new file mode 100644
index 00000000000..2c30c8bd240
--- /dev/null
+++ b/doc/builders/testers.chapter.md
@@ -0,0 +1,82 @@
+# Testers {#chap-testers}
+This chapter describes several testing builders which are available in the <literal>testers</literal> namespace.
+
+## `testVersion` {#tester-testVersion}
+
+Checks the command output contains the specified version
+
+Although simplistic, this test assures that the main program
+can run. While there's no substitute for a real test case,
+it does catch dynamic linking errors and such. It also provides
+some protection against accidentally building the wrong version,
+for example when using an 'old' hash in a fixed-output derivation.
+
+Examples:
+
+```nix
+passthru.tests.version = testVersion { package = hello; };
+
+passthru.tests.version = testVersion {
+  package = seaweedfs;
+  command = "weed version";
+};
+
+passthru.tests.version = testVersion {
+  package = key;
+  command = "KeY --help";
+  # Wrong '2.5' version in the code. Drop on next version.
+  version = "2.5";
+};
+```
+
+## `testEqualDerivation` {#tester-testEqualDerivation}
+
+Checks that two packages produce the exact same build instructions.
+
+This can be used to make sure that a certain difference of configuration,
+such as the presence of an overlay does not cause a cache miss.
+
+When the derivations are equal, the return value is an empty file.
+Otherwise, the build log explains the difference via `nix-diff`.
+
+Example:
+
+```nix
+testEqualDerivation
+  "The hello package must stay the same when enabling checks."
+  hello
+  (hello.overrideAttrs(o: { doCheck = true; }))
+```
+
+## `invalidateFetcherByDrvHash` {#tester-invalidateFetcherByDrvHash}
+
+Use the derivation hash to invalidate the output via name, for testing.
+
+Type: `(a@{ name, ... } -> Derivation) -> a -> Derivation`
+
+Normally, fixed output derivations can and should be cached by their output
+hash only, but for testing we want to re-fetch everytime the fetcher changes.
+
+Changes to the fetcher become apparent in the drvPath, which is a hash of
+how to fetch, rather than a fixed store path.
+By inserting this hash into the name, we can make sure to re-run the fetcher
+every time the fetcher changes.
+
+This relies on the assumption that Nix isn't clever enough to reuse its
+database of local store contents to optimize fetching.
+
+You might notice that the "salted" name derives from the normal invocation,
+not the final derivation. `invalidateFetcherByDrvHash` has to invoke the fetcher
+function twice: once to get a derivation hash, and again to produce the final
+fixed output derivation.
+
+Example:
+
+```nix
+tests.fetchgit = invalidateFetcherByDrvHash fetchgit {
+  name = "nix-source";
+  url = "https://github.com/NixOS/nix";
+  rev = "9d9dbe6ed05854e03811c361a3380e09183f4f4a";
+  sha256 = "sha256-7DszvbCNTjpzGRmpIVAWXk20P0/XTrWZ79KSOGLrUWY=";
+};
+```
diff --git a/doc/manual.xml b/doc/manual.xml
index e49ae67ec94..ccbaf40586d 100644
--- a/doc/manual.xml
+++ b/doc/manual.xml
@@ -25,6 +25,7 @@
   <title>Builders</title>
   <xi:include href="builders/fetchers.chapter.xml" />
   <xi:include href="builders/trivial-builders.chapter.xml" />
+  <xi:include href="builders/testers.chapter.xml" />
   <xi:include href="builders/special.xml" />
   <xi:include href="builders/images.xml" />
   <xi:include href="hooks/index.xml" />
diff --git a/pkgs/build-support/testers/default.nix b/pkgs/build-support/testers/default.nix
index e5a8dbc7960..8b79843b833 100644
--- a/pkgs/build-support/testers/default.nix
+++ b/pkgs/build-support/testers/default.nix
@@ -1,47 +1,8 @@
 { pkgs, lib, callPackage, runCommand }:
+# Documentation is in doc/builders/testers.chapter.md
 {
-
-  /* Checks that two packages produce the exact same build instructions.
-
-     This can be used to make sure that a certain difference of configuration,
-     such as the presence of an overlay does not cause a cache miss.
-
-     When the derivations are equal, the return value is an empty file.
-     Otherwise, the build log explains the difference via `nix-diff`.
-
-     Example:
-
-         testEqualDerivation
-           "The hello package must stay the same when enabling checks."
-           hello
-           (hello.overrideAttrs(o: { doCheck = true; }))
-  */
   testEqualDerivation = callPackage ./test-equal-derivation.nix { };
 
-  /* Checks the command output contains the specified version
-
-     Although simplistic, this test assures that the main program
-     can run. While there's no substitute for a real test case,
-     it does catch dynamic linking errors and such. It also provides
-     some protection against accidentally building the wrong version,
-     for example when using an 'old' hash in a fixed-output derivation.
-
-     Examples:
-
-       passthru.tests.version = testVersion { package = hello; };
-
-       passthru.tests.version = testVersion {
-         package = seaweedfs;
-         command = "weed version";
-       };
-
-       passthru.tests.version = testVersion {
-         package = key;
-         command = "KeY --help";
-         # Wrong '2.5' version in the code. Drop on next version.
-         version = "2.5";
-       };
-  */
   testVersion =
     { package,
       command ? "${package.meta.mainProgram or package.pname or package.name} --version",
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 5117ec4d309..1bcc20e2d2f 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -725,8 +725,8 @@ with pkgs;
 
   installShellFiles = callPackage ../build-support/install-shell-files {};
 
-  # See doc/builders/special/invalidateFetcherByDrvHash.section.md or
-  # https://nixos.org/manual/nixpkgs/unstable/#sec-pkgs-invalidateFetcherByDrvHash
+  # See doc/builders/testers.chapter.md or
+  # https://nixos.org/manual/nixpkgs/unstable/#tester-invalidateFetcherByDrvHash
   invalidateFetcherByDrvHash = f: args:
     let
       drvPath = (f args).drvPath;