add to news and docs

Author: IanButterworth

NEWS.md

@@ -19,6 +19,11 @@ New language features
 
 Language changes
 ----------------
+* Code coverage and malloc tracking is no longer generated during the package precompilation stage.
+  Further, during these modes pkgimage caches are now used for packages that are not being tracked.
+  Meaning that coverage testing (the default for `julia-actions/julia-runtest`) will by default use
+  pkgimage caches for all other packages than the package being tested, likely meaning faster test
+  execution. ([#52123])
 
 Compiler/Runtime improvements
 -----------------------------

stdlib/Test/docs/src/index.md

@@ -491,3 +491,15 @@ Using `Test.jl`, more complicated tests can be added for packages but this shoul
 ```@meta
 DocTestSetup = nothing
 ```
+
+### Code Coverage
+
+Code coverage tracking during tests can be enabled using the `pkg> test --coverage` flag (or at a lower level using the
+[`--code-coverage`](@ref command-line-interface) julia arg). This is on by default in the
+[julia-runtest](https://github.com/julia-actions/julia-runtest) GitHub action.
+
+To evaluate coverage either manually inspect the `.cov` files that are generated beside the source files locally,
+or in CI use the [julia-processcoverage](https://github.com/julia-actions/julia-processcoverage) GitHub action.
+
+!!! compat "Julia 1.11"
+    Since Julia 1.11, coverage is not collected during the package precompilation phase.