fix(coverage): merge duplicate reports (#8942)

Merging multiple runs isn't quite right because we 
rely on a 0 count to signal that a block hasn't been called.

Other tools like c8 expect this to be true as-well so we 
need to do our best to merge coverage files rather 
than duplicating them.

1 files changed, 31 insertions, 0 deletions

diff --git a/cli/tests/test_run_combined_coverage.out b/cli/tests/test_run_combined_coverage.out
new file mode 100644
index 000000000..476e9adcc
--- /dev/null
+++ b/cli/tests/test_run_combined_coverage.out
@@ -0,0 +1,31 @@
+Check [WILDCARD]/tests/$deno$test.ts
+running 2 tests
+test spawn test ... Check [WILDCARD]/tests/run_coverage.ts
+ok ([WILDCARD])
+test spawn test ... Check [WILDCARD]/tests/$deno$test.ts
+running 1 tests
+test returnsFooSuccess ... ok ([WILDCARD])
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out ([WILDCARD])
+
+ok ([WILDCARD])
+
+test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out ([WILDCARD])
+
+cover [WILDCARD]/tests/run_coverage.ts ... 100.000% (3/3)
+cover [WILDCARD]/tests/subdir/mod1.ts ... 57.143% (8/14)
+   8 | export function printHello3() {
+   9 |     printHello2();
+  10 | }
+  11 | export function throwsError() {
+  12 |     throw Error("exception from mod1");
+  13 | }
+cover [WILDCARD]/tests/subdir/print_hello.ts ... 25.000% (1/4)
+   1 | export function printHello() {
+   2 |     console.log("Hello");
+   3 | }
+cover [WILDCARD]/tests/subdir/subdir2/mod2.ts ... 62.500% (5/8)
+   5 | export function printHello2() {
+   6 |     printHello();
+   7 | }
+cover [WILDCARD]/tests/test_coverage.ts ... 100.000% (5/5)