Don't consider a failed build as a killed mutant

verify-coverage-mutants.fsx

@@ -12,6 +12,11 @@ type MutationCase =
       TestName: string
       DeclaringType: string }
 
+type MutationOutcome =
+    | Killed
+    | Survived
+    | BuildFailed
+
 type Command =
     | List
     | Show of string
@@ -203,15 +208,26 @@ let runMutation (mutation: MutationCase) =
     File.WriteAllText(targetFile, mutatedText)
 
     printfn "==> %s: %s" mutation.Id mutation.TestName
-    let exitCode = runProcess worktreePath "dotnet" [ "test"; testProjectPath; "--configuration"; options.Configuration; "--filter"; testFilter mutation; "--nologo" ]
-    File.WriteAllText(targetFile, originalText)
+    let buildExitCode =
+        runProcess worktreePath "dotnet" [ "build"; testProjectPath; "--configuration"; options.Configuration; "--nologo" ]
 
-    if exitCode = 0 then
-        printfn "SURVIVED  %s" mutation.Id
-        false
-    else
-        printfn "KILLED    %s" mutation.Id
-        true
+    let outcome =
+        if buildExitCode <> 0 then
+            printfn "BUILD FAILED %s" mutation.Id
+            BuildFailed
+        else
+            let testExitCode =
+                runProcess worktreePath "dotnet" [ "test"; testProjectPath; "--configuration"; options.Configuration; "--filter"; testFilter mutation; "--no-build"; "--nologo" ]
+
+            if testExitCode = 0 then
+                printfn "SURVIVED  %s" mutation.Id
+                Survived
+            else
+                printfn "KILLED    %s" mutation.Id
+                Killed
+
+    File.WriteAllText(targetFile, originalText)
+    outcome
 
 let mutations = mutationCases ()
 
@@ -234,13 +250,14 @@ match options.Command with
 
     try
         createWorktree ()
-        let killed =
+        let outcomes =
             requested
             |> List.map runMutation
-        let survivors = killed |> List.filter not |> List.length
-        if survivors = 0 then
+        let survivors = outcomes |> List.filter ((=) Survived) |> List.length
+        let buildFailures = outcomes |> List.filter ((=) BuildFailed) |> List.length
+        if survivors = 0 && buildFailures = 0 then
             printfn "All requested mutants were killed."
         else
-            fail $"{survivors} mutant(s) survived."
+            fail $"{survivors} mutant(s) survived. {buildFailures} mutant(s) failed to build."
     finally
         cleanup ()