ticker test: add test for set interrupt with timestamp in the past

2 test cases added, one for event in the past, one for event in future but very close
to the current time, thus once is set, it is already in the past, and we fire
interrupt immediately.

TESTS/mbed_hal/ticker/main.cpp

@@ -1986,6 +1986,58 @@ static void test_irq_handler_insert_non_immediate_in_irq()
     TEST_ASSERT_EQUAL(0, interface_stub.disable_interrupt_call);
 }
 
+static uint32_t ticker_interface_stub_read_interrupt_time()
+{
+    ++interface_stub.read_call;
+    // only if set interrupt call, to test the condition afterwards
+    if (interface_stub.set_interrupt_call) {
+        return interface_stub.interrupt_timestamp;
+    } else {
+        return interface_stub.timestamp;
+    }
+} 
+
+/**
+ * Test to insert an event that is already in the past, the fire_interrupt should
+ * be invoked, instead of set_interrupt
+ */
+static void test_set_interrupt_past_time()
+{
+    interface_stub.set_interrupt_call = 0;
+    interface_stub.fire_interrupt_call = 0;
+    interface_stub.timestamp = 0xFF;
+
+
+    // This tests fire now functinality when next_event_timestamp <= present
+    ticker_event_t event = { 0 };
+    const timestamp_t event_timestamp = interface_stub.timestamp;
+    const uint32_t id_last_event = 0xDEADDEAF;
+
+    ticker_insert_event(&ticker_stub, &event, event_timestamp, id_last_event);
+    TEST_ASSERT_EQUAL(0, interface_stub.set_interrupt_call);
+    TEST_ASSERT_EQUAL(1, interface_stub.fire_interrupt_call);
+}
+/**
+ * Test to insert an event that is being delayed, set_interrupt is set
+ * but then event is already in the past, thus fire_interrupt should be invoked right-away
+ */
+static void test_set_interrupt_past_time_with_delay()
+{
+    interface_stub.set_interrupt_call = 0;
+    interface_stub.fire_interrupt_call = 0;
+    interface_stub.timestamp = 0xFF;
+
+    // This tests fire now functionality when present time >= new_match_time
+    interface_stub.interface.read = ticker_interface_stub_read_interrupt_time;
+    ticker_event_t event = { 0 };
+    const timestamp_t event_timestamp = interface_stub.timestamp + 5;
+    const uint32_t id_last_event = 0xDEADDEAF;
+
+    ticker_insert_event(&ticker_stub, &event, event_timestamp, id_last_event);
+    TEST_ASSERT_EQUAL(1, interface_stub.set_interrupt_call);
+    TEST_ASSERT_EQUAL(1, interface_stub.fire_interrupt_call);
+}
+
 static const case_t cases[] = {
     MAKE_TEST_CASE("ticker initialization", test_ticker_initialization),
     MAKE_TEST_CASE(
@@ -2070,6 +2122,14 @@ static const case_t cases[] = {
     MAKE_TEST_CASE(
         "test_irq_handler_insert_non_immediate_in_irq", 
         test_irq_handler_insert_non_immediate_in_irq
+    ),
+    MAKE_TEST_CASE(
+        "test_set_interrupt_past_time", 
+        test_set_interrupt_past_time
+    ),
+    MAKE_TEST_CASE(
+        "test_set_interrupt_past_time_with_delay", 
+        test_set_interrupt_past_time_with_delay
     )
 };