A mock framework for use with SVUnit
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Creating an SVMock

This goes through the working example in examples/class/bedrock. Best to refer to files in that directly as you read through this. This assumes that you have an understanding of SVUnit. If you don't, you probably want to start at the SVUnit project page first, then come back to this.

In this example, we're unit testing a class called bedrock. There's one function in bedrock that needs to be unit tested called yabba_dabba_do. Specifically, we're interested in how bedrock::yabba_dabba_do() relies on functionality from an instance of flintstones. Instead of using the real version of flintstones, we'll use SVMock to create a flinstones_mock so we can directly isolate and test the interactions within bedrock.

Defining a Class

The class flintstones includes 3 functions used by bedrock: dino, pebbles and bam_bam...

class flintstones;
  function new(); endfunction

  virtual function void dino();
    // all the code for dino

  virtual function int pebbles(int fred, string wilma [int]);
    return 12;

  virtual function void bam_bam(int barney);
    // nothing to do

Mocking a Class

To create a mock of flintstones, we'll use macros defined in svmock_defines.svh as such...

`SVMOCK(mock_flintstones, flintstones)

  `SVMOCK_FUNC2(pebbles, int, /*input*/, int,    fred,  /*scalar*/, /*no-default*/,
                              /*input*/, string, wilma, [int],      /*no-default*/)

  `SVMOCK_VFUNC1(bam_bam, /*input*/, int, barney, /*scalar*/, /*no-default*/)

The SVMOCK(mock_class, parent_class)/SVMOCK_END macros roughly translate to class/endclass.

Each function in flintstones is mocked with an SVMOCK_* function macro. Void functions use the SVMOCK_VFUNC<N> macros where 'N' is the number of input arguments. The function flintstones::dino, for example, has no input arguments so it is mocked with SVMOCK_VFUNC0 whereas flintstones::bam_bam has 1 argument so it requires the SVMOCK_VFUNC1 macro. The first argument to the void function macros is the name of the function. Subsequent arguments are related to each input argument.

For functions that are non-void, the SVMOCK_FUNC\<N\> macros are used. The first argument is still the name of the function. The second argument is the return type of the function. Subsequent arguments are related to each input argument.

Tasks are mocked using the `SVMOCK_TASK<N> macors. The task macro syntax is the same as the void function macros.


The has inputs to cover all possible ways to declare a function/task argument. The syntax is:

|          Direction       | Type | Name |     Aggregate type    |     Default     |
| [input|ref|output|inout] | type | name | [aggregate data type] | [default value] |

All inputs are required for each function/task argument (to maintain the order of the macro inputs). However, direction, aggregate type and default can take an empty string input in cases where they aren't necessary. To make it easier to maintain argument order, it's recommended to use comments for unnecessary inputs. For example, the arguments to pebbles are broken into macro arguments as...

Direction Type Name Aggregate type Default
/*input*/ int fred /*scalar*/ /*no-default*/
/*input*/ string wilma [int] /*no-default*/

Connecting The Mock

With bedrock defined as...

class bedrock;
  flintstones f = new();

  function void yabba_dabba_do(string wilma [int]);
    f.bam_bam(f.pebbles(wilma.num(), wilma));

...to take effect, an instance of flintstones_mock must be created and used in place of the original bedrock::f. This can be done in the bedrock_unit_test.sv where it's declared as our unit under test uut.

  `include "flintstones_mock.sv"
  bedrock uut;
  mock_flintstones mock_f = new();
  function void build();
    svunit_ut = new(name);

    uut = new();
    uut.f = mock_f;

The flinstones_mock has to be included for compilation, either as an include or as part of a package. In this example we're using an include (see above).

It's also required that the reseting and checking of the mock be invoked inside the unit test template. That's best done in the setup() and teardown() methods so that it's automatically done for every test.

  task setup();
    /* Place Setup Code Here */

  task teardown();
    /* Place Teardown Code Here */


Using The Mock

Currently, users can set expectations for how many times a function has been called as well as the arguments it is invoked with. You can also override function return values.

Expect Functions Are Invoked

In our first unit test, we simply want to verify that the function dino() is invoked in bedrock::yabba_dabba_do. We can do that with an EXPECT_CALL.

    `EXPECT_CALL(mock_f, dino).exactly(1); // dino should be called exactly once


Since we expect dino() to be called exactly once, we use exactly(1). Other options for an EXPECT_CALL that verifies whether or not a function has been called are at_least(<N>), at_most(<N>) and between(<N>, <M>).

EXPECT_CALL method Check
exactly(N) function is called exactly 'N' times
at_least(N) function is called at least 'N' times
at_most(N) function is called at most 'N' times
between(N, M) function is called at least 'N' and at most 'M' times

Expect Function Arguments

We can also use a flintstones_mock EXPECT_CALL to check functions are called with specific arguments. For example, we can expect that f.pebbles is invoked from yabba_dabba_do with arguments derived from its input argument. Setting expectations for arguments is done with a with_args EXPECT_CALL.

    `EXPECT_CALL(mock_f, pebbles).with_args(betty.num(), betty); // expect yabba_dabba_do invokes pebbles(betty.num(), betty)


Inputs to with_args are identical to the inputs of the function being checked. In this case, we're checking inputs to pebbles which are (int , string [int]) so with_args has the same (int , string [int]) inputs. Currently, all inputs must be specified.

Overriding Return Values

The mock can be used to override return values of functions. In a third test, we want to confirm bam_bam() is invoked with the return value of pebbles() without concerning ourselves with the actual functionality of pebbles or it's realistic return value. We can use ON_CALL to to override the return value of pebbles(), then use EXPECT_CALL to verify that the value we specify is indeed used as input to bam_bam().

    `ON_CALL(mock_f, pebbles).returns(99);         // Override pebbles return value
    `EXPECT_CALL(mock_f, bam_bam).with_args(99);   // expect bam_bam is called with the override value


Overriding A Method

If simply overriding a return value isn't enough or you need to replace functionality of a method, you can override that mocked method with something entirely new. For example, the functionality of dino() could replaced by calling mr_slate() instead. To do this, we need to define mr_slate() then map it to dino() with an SVMOCK_MAP_FUNC in flintstones_mock.

  `SVMOCK_MAP_VFUNC0(dino, mr_slate)
  bit mr_slate_instead;
  function void mr_slate();
    mr_slate_instead = 1;

Once mr_slate() is mapped to dino(), we can then override dino() in our 4th unit test using a will_by_default ON_CALL. Notice that will_by_default takes a string input which is the name of the newly mapped function.

    `ON_CALL(mock_f, dino).will_by_default("mr_slate");

Important to note that the signature of mr_slate() is exactly the same as the signature for dino() (i.e. neither function has input arguments). For another example, if we were to map pebbles() to a new function called rock_quarry(), rock_quarry() would require similar fred and wilma input arguments.

  `SVMOCK_FUNC2(pebbles, int, int, fred, , string, wilma, [int])
  `SVMOCK_MAP_FUNC2(pebbles, rock_quarry)
  function int rock_quarry(int fred, string wilma [int]);
    // a replacement for pebbles

There's a different macro available for each possible method type.


Initialization and Checking

To ensure the mock state is reset for each test, the clear() function for the mock should be called in the setup() method of the unit test template. Similarly, for the checking to be invoked it's necessary to call the verify() function in the mock. verify() will return 1 (true) when expectations are met, 0 (false) otherwise). It's recommended you can call verify() in the teardown method so it's automatically invoked at the end of each test.

Future Development

We're at the tip of the ice berg here so there's more to come.


Feel free to send comments and/or critique to neil.johnson@agilesoc.com. Optionally, you can file issues at https://github.com/nosnhojn/svmock/issues.