pw_assert: Initial assert module

This starts the assert and assert_basic modules, which are the beginning
of our assert foundation. Much more is needed; in particular the "tests"
don't really do much other than check for compilation.

Screenshot
==========

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  Welp, that didn't go as planned. It seems we crashed. Terribly sorry!

  CRASH MESSAGE

     Check failed: x (=50) > y (=51300): You SHOULD see this message

  CRASH FILE & LINE

     ../../pw_assert/assert_test.cc:46

  CRASH FUNCTION

     PigweedTestBody

==========

Change-Id: I9dbb460b3b33040d8009749f44b9fc174e2c8138
diff --git a/pw_assert/assert_test.c b/pw_assert/assert_test.c
new file mode 100644
index 0000000..a309cf0
--- /dev/null
+++ b/pw_assert/assert_test.c
@@ -0,0 +1,137 @@
+// Copyright 2020 The Pigweed Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+// This is "test" verifies that the assert backend:
+//
+// - Compiles as plain C
+//
+// Unfortunately, this doesn't really test the crashing functionality since
+// that is so backend dependent.
+//
+// NOTE: To run these tests for pw_assert_basic, you must modify two things:
+//
+//   (1) Set DISABLE_ASSERT_TEST_EXECUTION 1 in assert_test.cc (this file)
+//   (1) Set DISABLE_ASSERT_TEST_EXECUTION 1 in assert_test.c
+//   (2) Set PW_ASSERT_BASIC_DISABLE_NORETURN 1 in assert_basic.h
+//
+// This is obviously not a long term solution.
+
+#include "pw_assert/assert.h"
+
+#ifdef __cplusplus
+#error "This file must be compiled as plain C to verify C compilation works."
+#endif  // __cplusplus
+
+// This is a global constant to feed into the formatter for tests.
+// Intended to pair with FAIL_IF_DISPLAYED_ARGS or FAIL_IF_HIDDEN_ARGS.
+static const int z = 10;
+
+// At some point in the future when there is a proper test system in place for
+// crashing, the below strings can help indicate pass/fail for a check.
+
+#define FAIL_IF_DISPLAYED "FAIL IF DISPLAYED"
+#define FAIL_IF_DISPLAYED_ARGS "FAIL IF DISPLAYED: %d"
+
+#define FAIL_IF_HIDDEN "FAIL IF HIDDEN"
+#define FAIL_IF_HIDDEN_ARGS "FAIL IF HIDDEN: %d"
+
+// This switch exists to support compiling and/or running the tests.
+#define DISABLE_ASSERT_TEST_EXECUTION 1
+#if DISABLE_ASSERT_TEST_EXECUTION
+#define MAYBE_SKIP_TEST return
+#else
+#define MAYBE_SKIP_TEST ;
+#endif
+
+static int Add3(int a, int b, int c) { return a + b + c; }
+
+void AssertTestsInC() {
+  {  // TEST(Crash, WithAndWithoutMessageArguments)
+    MAYBE_SKIP_TEST;
+    PW_CRASH(FAIL_IF_HIDDEN);
+    PW_CRASH(FAIL_IF_HIDDEN_ARGS, z);
+  }
+
+  {  // TEST(Check, NoMessage)
+    MAYBE_SKIP_TEST;
+    PW_CHECK(1);
+    PW_CHECK(0);
+  }
+
+  {  // TEST(Check, WithMessageAndArgs)
+    MAYBE_SKIP_TEST;
+    PW_CHECK(1, FAIL_IF_DISPLAYED);
+    PW_CHECK(1, FAIL_IF_DISPLAYED_ARGS, z);
+
+    PW_CHECK(0, FAIL_IF_HIDDEN);
+    PW_CHECK(0, FAIL_IF_HIDDEN_ARGS, z);
+  }
+
+  {  // TEST(Check, IntComparison)
+    MAYBE_SKIP_TEST;
+    int x_int = 50;
+    int y_int = 66;
+
+    PW_CHECK_INT_LE(x_int, y_int);
+    PW_CHECK_INT_LE(x_int, y_int, "INT: " FAIL_IF_DISPLAYED);
+    PW_CHECK_INT_LE(x_int, y_int, "INT: " FAIL_IF_DISPLAYED_ARGS, z);
+
+    PW_CHECK_INT_GE(x_int, y_int);
+    PW_CHECK_INT_GE(x_int, y_int, "INT: " FAIL_IF_HIDDEN);
+    PW_CHECK_INT_GE(x_int, y_int, "INT: " FAIL_IF_HIDDEN_ARGS, z);
+  }
+
+  {  // TEST(Check, UintComparison)
+    MAYBE_SKIP_TEST;
+    unsigned int x_uint = 50;
+    unsigned int y_uint = 66;
+
+    PW_CHECK_UINT_LE(x_uint, y_uint);
+    PW_CHECK_UINT_LE(x_uint, y_uint, "UINT: " FAIL_IF_DISPLAYED);
+    PW_CHECK_UINT_LE(x_uint, y_uint, "UINT: " FAIL_IF_DISPLAYED_ARGS, z);
+
+    PW_CHECK_UINT_GE(x_uint, y_uint);
+    PW_CHECK_UINT_GE(x_uint, y_uint, "UINT: " FAIL_IF_HIDDEN);
+    PW_CHECK_UINT_GE(x_uint, y_uint, "UINT: " FAIL_IF_HIDDEN_ARGS, z);
+  }
+
+  {  // TEST(Check, FloatComparison)
+    MAYBE_SKIP_TEST;
+    float x_float = 50.5;
+    float y_float = 66.5;
+
+    PW_CHECK_FLOAT_LE(x_float, y_float);
+    PW_CHECK_FLOAT_LE(x_float, y_float, "FLOAT: " FAIL_IF_DISPLAYED);
+    PW_CHECK_FLOAT_LE(x_float, y_float, "FLOAT: " FAIL_IF_DISPLAYED_ARGS, z);
+
+    PW_CHECK_FLOAT_GE(x_float, y_float);
+    PW_CHECK_FLOAT_GE(x_float, y_float, "FLOAT: " FAIL_IF_HIDDEN);
+    PW_CHECK_FLOAT_GE(x_float, y_float, "FLOAT: " FAIL_IF_HIDDEN_ARGS, z);
+  }
+
+  {  // TEST(Check, ComparisonArgumentsWithCommas)
+    MAYBE_SKIP_TEST;
+    int x_int = 50;
+    int y_int = 66;
+
+    PW_CHECK_INT_LE(Add3(1, 2, 3), y_int);
+    PW_CHECK_INT_LE(x_int, Add3(1, 2, 3));
+
+    PW_CHECK_INT_LE(Add3(1, 2, 3), y_int, FAIL_IF_DISPLAYED);
+    PW_CHECK_INT_LE(x_int, Add3(1, 2, 3), FAIL_IF_DISPLAYED_ARGS, z);
+
+    PW_CHECK_INT_LE(Add3(1, 2, 3), Add3(1, 2, 3), "INT: " FAIL_IF_DISPLAYED);
+    PW_CHECK_INT_LE(x_int, y_int, "INT: " FAIL_IF_DISPLAYED_ARGS, z);
+  }
+}