test: set case name from initial filename for a sequence

Port more incremental tests.

test/incremental/assert_function.5.zig

@@ -0,0 +1,19 @@
+pub fn main() void {
+    assert(add(3, 4) == 7);
+    assert(add(20, 10) == 30);
+}
+
+fn add(a: u32, b: u32) u32 {
+    var x: u32 = undefined;
+    x = 0;
+    x += a;
+    x += b;
+    return x;
+}
+
+pub fn assert(ok: bool) void {
+    if (!ok) unreachable; // assertion failure
+}
+
+// run
+//