tests/channels: add tests for built-in cap function

Author: mertcandav

tests/channels/main.jule

@@ -55,10 +55,26 @@ fn blockingSelect() {
 	}
 }
 
+fn capacity() {
+	mut ch := make(chan int, 90)
+	if cap(ch) != 90 {
+		panic("expected 90")
+	}
+	ch = make(chan int)
+	if cap(ch) != 0 {
+		panic("expected 0")
+	}
+	ch = nil
+	if cap(ch) != 0 {
+		panic("expected 0")
+	}
+}
+
 fn main() {
 	rangeIteration()
 	unbuffered()
 	sendOnly()
 	recvOnly()
 	blockingSelect()
+	capacity()
 }