lib/init-exe, lib/init-lib: ensure tests runs again

After commit ede5dcf (make the build runner and test runner talk to each other),
the std.Build.addTest function no longer runs tests, but the build.zig
files in init-exe and init-lib where not updated.

Rename main_tests to lib_tests and "Run library tests" to "Run unit tests",
for consistency with init-exe.

Use the new Build.addRunArtifact function, instead of the deprecated
CompileStep.run method.

Add a RunStep to exe_tests and lib_tests.

In the addCliTests function in tests/test.zig:
  - set the new RunStep.is_test_command field to true, when running the
    `zig build test` command.  See ziglang#15104.

  - Remove an empty line in the addCliTests function in tests/tests.zig.

Closes ziglang#15009

Author: perillo

lib/init-exe/build.zig

@@ -32,7 +32,7 @@ pub fn build(b: *std.Build) void {
     // This *creates* a RunStep in the build graph, to be executed when another
     // step is evaluated that depends on it. The next line below will establish
     // such a dependency.
-    const run_cmd = exe.run();
+    const run_cmd = b.addRunArtifact(exe);
 
     // By making the run step depend on the install step, it will be run from the
     // installation directory rather than directly from within the cache directory.
@@ -59,9 +59,12 @@ pub fn build(b: *std.Build) void {
         .optimize = optimize,
     });
 
+    // A RunStep must be added to run the unit tests.
+    const run_test = b.addRunArtifact(exe_tests);
+
     // Similar to creating the run step earlier, this exposes a `test` step to
     // the `zig build --help` menu, providing a way for the user to request
     // running the unit tests.
     const test_step = b.step("test", "Run unit tests");
-    test_step.dependOn(&exe_tests.step);
+    test_step.dependOn(&run_test.step);
 }

lib/init-lib/build.zig

@@ -30,15 +30,18 @@ pub fn build(b: *std.Build) void {
     lib.install();
 
     // Creates a step for unit testing.
-    const main_tests = b.addTest(.{
+    const lib_tests = b.addTest(.{
         .root_source_file = .{ .path = "src/main.zig" },
         .target = target,
         .optimize = optimize,
     });
 
+    // A RunStep must be added to run the unit tests.
+    const run_test = b.addRunArtifact(lib_tests);
+
     // This creates a build step. It will be visible in the `zig build --help` menu,
     // and can be selected like this: `zig build test`
     // This will evaluate the `test` step rather than the default, which is "install".
-    const test_step = b.step("test", "Run library tests");
-    test_step.dependOn(&main_tests.step);
+    const test_step = b.step("test", "Run unit tests");
+    test_step.dependOn(&run_test.step);
 }

test/tests.zig

@@ -663,7 +663,6 @@ pub fn addCliTests(b: *std.Build) *Step {
     const s = std.fs.path.sep_str;
 
     {
-
         // Test `zig init-lib`.
         const tmp_path = b.makeTempPath();
         const init_lib = b.addSystemCommand(&.{ b.zig_exe, "init-lib" });